onslaught
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C1 noun /ˈɒn.slɔːt/

onslaught

猛攻
Meaning
A fierce or destructive attack.
Example
The village faced an onslaught of enemy forces.
その村は敵軍の猛攻に直面しました。
C1 verb /ˌaʊtˈstrɛtʃ/

outstretch

外に伸ばす
Meaning
To extend or stretch something outward.
Example
He outstretched his hand to help her up.
彼は彼女を助けるために手を差し出した。
B2 noun /ˈɔr.fən/

Orphan

孤児
Meaning
a child whose parents are dead; someone without protective support
Example
The orphan was adopted by a loving family.
その孤児は愛情深い家族に養子として迎えられました。
C1 noun /ˈɔr.ə.tər/

Orator

演説家
Meaning
a public speaker, especially one who is eloquent or skilled in speaking
Example
The famous orator delivered an inspiring speech.
有名な演説家が感動的なスピーチを行った。
B2 noun ˈəʊ.və.hed

overhead

間接費
Meaning
Ongoing business expenses not directly attributable to creating a product or service.
Example
The company reduced its overhead to increase profits.
会社は利益を増やすために間接費を削減した。
A2 noun /ɔɪl/

Oil

油
Meaning
a viscous liquid derived from petroleum or plants, used for cooking or fuel
Example
Heat the oil in a pan before adding the vegetables.
野菜を加える前にフライパンで油を温めます。
C2 verb /ˈoʊɡəl/

ogle

じっと見る
Meaning
To look at someone with obvious sexual interest.
Example
He kept ogling the models on the runway.
彼はランウェイのモデルたちを見続けた。
C1 adjective /əbˈdʒek.ʃən.ə.bəl/

Objectionable

不快な
Meaning
arousing distaste or opposition; unpleasant or offensive
Example
His objectionable behavior made everyone uncomfortable.
彼の不快な行動は、皆を不快にさせた。
B1 verb /əˈkɜːr/

occur

発生する
Meaning
to happen or take place; to be found or present
Example
The accident occurred at the intersection during rush hour.
事故はラッシュアワーの交差点で発生しました。
B2 adjective, verb /əbˈskjʊr/

obscure

不明確
Meaning
Not clearly expressed or understood; to make something difficult to see or understand.
Example
The meaning of the poem was obscure to most readers.
詩の意味はほとんどの読者には不明確でした。
A2 noun /ˈɒpərə/

opera

オペラ
Meaning
a dramatic performance in which the actors sing most of their lines
Example
We watched a beautiful opera at the theater last night.
昨晩、劇場で美しいオペラを観ました。
B2 noun /ɒdz/

odds

確率
Meaning
the likelihood or probability of something happening; chances for or against something
Example
The odds of winning the lottery are very low.
宝くじに当選する確率は非常に低いです。
C2 noun /ˈɔːfəl/

offal

内臓
Meaning
the internal organs and entrails of an animal used as food; waste parts
Example
The butcher prepared sausages using pork offal.
肉屋は豚の臓物を使ってソーセージを作った。
A1 preposition /ʌv/

of

の
Meaning
expressing the relationship between a part and a whole
Example
The book is on the table, in front of the window.
本はテーブルの上にあり、窓の前にあります。
B2 adjective ɔːrˈɡæn.ɪk

organic

有機
Meaning
Produced or involving production without the use of chemical fertilizers, pesticides, or other artificial agents.
Example
Organic farming improves soil health and reduces pollution.
有機農業は土壌の健康を改善し、汚染を減少させます。
C2 noun /ˌɑːpərˈtuːnɪzəm/

opportunism

機会主義
Meaning
The practice of taking advantage of opportunities regardless of principles or ethics.
Example
His decision was driven by opportunism, not values.
彼の決定は、価値観ではなくオポチュニズムに動機づけられていました。
C1 noun ɔːrˈdiːl

ordeal

厳しい試練
Meaning
A physical or mental painful experience that must be endured
Example
Surviving the wilderness was a tough ordeal for them.
荒野で生き残ることは彼らにとって大変な試練でした。
C1 noun ˌɒp.tɪ.maɪˈzeɪ.ʃən

optimization

最適化
Meaning
Improving processes to increase performance and efficiency.
Example
SEO optimization helps websites rank higher on search engines.
SEO最適化はウェブサイトが検索エンジンでより高いランクを獲得するのを助けます。
C1 noun/verb /ˈoʊvərˌhæŋ/

overhang

突出部
Meaning
To extend outward and hang over something; a projecting part.
Example
The roof overhang provides shade in the summer.
屋根のオーバーハングは夏に日陰を提供します。
C1 verb /ˈɒfsɛt/

offset

相殺
Meaning
To counterbalance or compensate for something.
Example
The company's losses were offset by gains in other departments.
会社の損失は他の部門での利益で相殺されました。
A2 adjective /ˈɒb.vi.əs/

Obvious

明白な; 簡単に理解できる
Meaning
easily perceived or understood; clear and apparent to the mind
Example
It was obvious that she was upset about something.
それは彼女が何かについて不満を抱えていることが明らかでした。
B2 noun /ˈoʊvərpæs/

overpass

高架橋
Meaning
A bridge that carries one road or railway over another.
Example
The new overpass reduced traffic congestion in the city.
新しい高架橋は市内の交通渋滞を減らしました。
C2 noun /ɔːrˈθɑːɡrəfi/

orthography

正書法
Meaning
The conventional spelling system of a language.
Example
English orthography can be confusing for learners.
英語の正書法は学習者にとって混乱を招くことがあります。
C1 verb ˈɔːr.kɪ.streɪt

orchestrate

調整する
Meaning
To plan or coordinate the elements of (a situation) to produce a desired effect, especially surreptitiously.
Example
He skillfully orchestrated the entire event.
彼は巧妙に全体のイベントを調整しました。
C1 noun /ɔːr/

Oar

オール
Meaning
a long pole with a flat blade used to row a boat
Example
He dipped the oar into the water and pulled the boat forward.
彼はオールを水に浸し、ボートを前に進めた。
C1 adjective /ˈɔːrθədɑːks/

orthodox

Meaning
conforming to traditional beliefs or practices
Example
He comes from a very orthodox family.
C1 noun /ˈoʊvərˌtoʊn/

overtone

微妙な意味
Meaning
A subtle quality, implication, or additional meaning beyond the obvious.
Example
His speech had political overtones that were hard to ignore.
彼のスピーチには無視できない政治的なニュアンスが含まれていました。
C1 noun ˈoʊʃən əˌsɪdɪfɪˈkeɪʃən

ocean acidification

海洋酸性化
Meaning
The ongoing decrease in the pH of the Earth's oceans, caused by the absorption of carbon dioxide from the atmosphere.
Example
Ocean acidification is caused by atmospheric CO2 absorption.
海洋酸性化は、大気中のCO2の吸収によって引き起こされます。
B2 noun /ˌɑb.zɚˈveɪ.ʃən/

Observation

観察
Meaning
the action of watching something carefully; a comment or remark
Example
The scientist made careful observations of the experiment.
科学者は実験を慎重に観察しました。
C2 noun /ˈɔːrzmən/

Oarsman

オールマン
Meaning
a person who rows a boat, especially as a member of a racing crew
Example
The experienced oarsman rowed the boat across the river.
経験豊富なオールマンは川を渡るためにボートを漕いだ。
C1 verb /ˌoʊvərˈriːtʃ/

overreach

過剰な努力
Meaning
to go beyond what is proper, acceptable, or achievable; to overextend
Example
The politician overreached by making promises he couldn't keep.
その政治家は約束を守れなかったことで過剰な努力をしました。
C1 noun əˈblɪv.i.ən

oblivion

忘却, 破壊, 消失
Meaning
The state of being unaware or unconscious of what is happening; complete forgetfulness.
Example
His name faded into oblivion over time.
彼の名前は時と共に忘却の中に消えた。
C1 verb /ˌoʊvərˈrʌn/

overrun

侵略する
Meaning
to spread over or occupy completely; to exceed a limit or time
Example
The garden was overrun with weeds.
庭は雑草に覆われていた。
B1 noun /ˈɑp.ʃən/

Option

オプション
Meaning
a thing that is or may be chosen; an alternative course of action
Example
You have the option to work from home or office.
自宅またはオフィスから仕事をするオプションがあります。
B2 verb /ɒpt/

opt

選ぶ
Meaning
to choose or decide to do something instead of something else
Example
Many students opt to study abroad for better opportunities.
多くの学生がより良い機会のために海外で学ぶことを選択します。
C2 noun /əˈprəʊ.bri.əm/

opprobrium

非難, 恥辱
Meaning
Harsh criticism or public disgrace.
Example
The scandal brought opprobrium on the politician.
スキャンダルは政治家に非難を浴びせた。
C2 verb /ˈɑːblɪˌɡeɪt/

obligate

強制する
Meaning
to bind legally or morally; to compel someone to do something
Example
The contract obligates the company to provide timely service.
契約は会社にタイムリーなサービスを提供することを義務付けます。
C1 noun /oʊˈveɪʃən/

ovation

拍手
Meaning
an enthusiastic show of approval, especially by clapping hands
Example
The actor received a standing ovation after his performance.
俳優はパフォーマンス後にスタンディングオベーションを受けました。
C1 noun /əˈpreʃ.ən/

Oppression

抑圧; 虐待; 圧政;
Meaning
cruel or unjust treatment or exercise of authority; the state of being subject to harsh treatment
Example
The people fought against political oppression.
人々は政治的な抑圧に反対して戦った。
C2 adjective /ˈoʊ.vɔɪd/

ovoid

卵型
Meaning
egg-shaped; resembling an oval or ellipse
Example
The artist painted an ovoid shape in the center of the canvas.
アーティストはキャンバスの中央に卵型の形を描きました。
C1 verb /ˌaʊtˈweɪ/

outweigh

より重要である
Meaning
To be more important, valuable, or significant than something else.
Example
The benefits of the new policy outweigh the risks.
新しい政策の利益はリスクを上回っています。
A2 adjective /ˈɔː.dɪ.nər.i/

Ordinary

普通の; 一般的な; 特別ではない
Meaning
normal; usual; not special
Example
It was just an ordinary day at the office.
それはオフィスでのただの普通の日でした。
C2 noun /əbˈstrʌkʃənɪst/

obstructionist

Meaning
a person who deliberately delays or prevents progress by being uncooperative or oppositional
Example
The obstructionist in the committee kept delaying the decision-making process.
B2 noun /oʊk/

oak

オークの木
Meaning
a large tree that produces acorns and has strong, hard wood
Example
The old oak tree provided shade for the entire yard.
古いオークの木は庭全体に日陰を提供しました。
C2 adjective /əˈprəʊ.bri.əs/

opprobrious

侮辱的な
Meaning
Expressing strong criticism or scorn.
Example
He made opprobrious remarks about his opponent.
彼は対戦相手に対して侮辱的な発言をしました。
C1 verb /əˈfɪʃieɪt/

officiate

執り行う
Meaning
To perform official duties, especially in a ceremony or as a referee.
Example
The priest will officiate the wedding ceremony.
司祭が結婚式を司る。
A2 noun /ˈɒm.lət/

Omelet

オムレツ
Meaning
a dish made from beaten eggs cooked in a frying pan and often folded around a filling
Example
She made a cheese omelet for breakfast.
彼女は朝食にチーズオムレツを作った。
C2 noun /ɒmˈnɪʃəns/

omniscience

全知
Meaning
the state of knowing everything
Example
The novel's narrator has an air of omniscience, revealing every character's thoughts.
小説の語り手は全知の空気をまとい、すべてのキャラクターの考えを明らかにしている。
C1 adjective /ˈɒptɪk/

optic

視覚の
Meaning
Relating to the eye or vision.
Example
The optic nerve carries signals from the eye to the brain.
視神経は目から脳に信号を伝達します。
C2 noun /ˈoʊɡər/

ogre

Meaning
A mythical monster, often depicted as large, hideous, and cruel; metaphorically, a cruel or terrifying person.
Example
The villagers feared the ogre who lived in the dark forest.
A2 noun /ˈoʊ.ʃən/

ocean

海洋
Meaning
A very large expanse of sea, especially the main areas of sea between continents.
Example
The ocean covers more than 70% of the Earth's surface.
海洋は地球の表面の70％以上を覆っています。
C2 noun /ˈɒn.rʌʃ/

onrush

突発的な流れ
Meaning
A sudden powerful forward or downward rush or flow.
Example
The onrush of water swept away the bridge.
水の突発的な流れが橋を流しました。
C1 noun /əˈkɜr.əns/

Occurrence

出来事
Meaning
an instance or event of something happening; the fact of occurring
Example
The occurrence of earthquakes is common in this region.
この地域では地震の出来事が一般的です。
C2 adjective /əˈfɪʃəs/

officious

干渉的な
Meaning
Excessively eager to offer unwanted help or advice; meddlesome.
Example
The officious guard kept interrupting the visitors with unnecessary instructions.
その干渉的な警備員は訪問者に不必要な指示で何度も中断させた。
C2 adjective /ˈɒkjʊlər/

ocular

眼科の
Meaning
Relating to the eye or vision.
Example
The patient was referred to a specialist for ocular treatment.
患者は眼科専門医に紹介されました。
C1 noun /ˌɑːsɪˈleɪʃən/

oscillation

振動
Meaning
The movement back and forth at a regular speed.
Example
The oscillation of the pendulum controls the clock.
振り子の振動が時計を制御します。
B2 verb /ˌoʊvərˈpeɪ/

overpay

過剰に支払う
Meaning
To pay more than is necessary or reasonable.
Example
She realized she had overpaid for the concert tickets.
彼女はコンサートのチケットに多く支払ったことに気づきました。
B2 adverb /əˈfɪʃəli/

officially

公式に
Meaning
in a formal or authorized way
Example
The building was officially opened by the mayor.
その建物は市長によって公式に開かれました。
C2 noun /əbˈstɛtrɪks/

obstetrics

産科
Meaning
The branch of medicine dealing with childbirth and care of women giving birth.
Example
She is studying obstetrics to become a specialist in childbirth.
彼女は産科を学んで、出産専門医になろうとしている。
C1 adjective /əbˈsɛsɪv/

obsessive

執着的
Meaning
Relating to or characterized by an obsession; thinking about something too much.
Example
He has an obsessive interest in cleanliness.
彼は清潔さに執着的な興味を持っています。
C1 noun /oʊˈeɪ.sɪs/

Oasis

オアシス
Meaning
a fertile spot in a desert where water is found; a pleasant refuge
Example
The travelers found an oasis after days in the desert.
旅行者たちは砂漠で数日後にオアシスを見つけました。
C1 adjective /ˈəʊnərəs/

onerous

重い
Meaning
involving a great deal of effort, difficulty, or burden
Example
Fulfilling the contract proved to be an onerous task for the company.
契約を履行することは会社にとって負担の大きい仕事だと証明された。
B2 adjective /ˌɑːp.təˈmɪs.tɪk/

optimistic

楽観的
Meaning
hopeful and confident about the future
Example
She is optimistic about the success of her new project.
彼女は新しいプロジェクトの成功に楽観的です。
C1 adjective /ˌəʊ.vərˈɑː.tʃɪŋ/

overarching

全体的な, 包括的な, 包み込む
Meaning
Comprehensive or all-embracing; forming an arch over something.
Example
The overarching theme of the book is human resilience.
その本の大きなテーマは人間の回復力です。
C1 noun /ˈɔːr.ə.tɔːr.i/

oratory

弁論術
Meaning
The art of public speaking; skilled and confident delivery of speeches to an audience.
Example
His exceptional oratory skills won him the debate competition.
彼の卓越した弁論術は、ディベートコンペティションで彼に勝利をもたらしました。
B2 noun /ˈɒkjʊpənt/

occupant

乗客
Meaning
A person who resides in or is present in a house, vehicle, seat, or place.
Example
The car had three occupants at the time of the accident.
事故の時、車には三人の乗客がいました。
C1 adjective /ˌəʊvərˈstɪmjʊˌleɪtɪd/

overstimulated

Meaning
Excessively excited or aroused, overwhelmed by too much stimulus.
Example
Overstimulated minds can lead to burnout and decreased productivity.
C2 verb /ˈɑːbvieɪt/

obviate

排除する
Meaning
To remove a need or difficulty; to prevent or avoid something.
Example
This new system obviates the need for manual data entry.
この新しいシステムは手動データ入力の必要性を排除します。
B1 adverb /əˈkeɪʒənəli/

Occasionally

時々; たまに;
Meaning
sometimes; from time to time; not regularly
Example
I occasionally visit my grandmother on weekends.
私は時々週末に祖母を訪ねます。
C2 adjective /ˌɔːfˈkiː/

off-key

外れた音
Meaning
out of tune; not in accordance with expected standards
Example
The singer was slightly off-key during the performance.
歌手はパフォーマンス中に少し外れた音だった。
C1 verb /ɔːrˈdeɪn/

ordain

Meaning
To officially make someone a priest or minister; to decree or order something officially.
Example
The bishop will ordain three new priests this Sunday.
B2 noun ˈəʊnəʃɪp

ownership

所有権
Meaning
The act, state, or right of possessing something; legal title to something.
Example
Ownership of resources was crucial.
資源の所有権は重要でした。
C2 noun /oʊd/

ode

オード
Meaning
a lyrical poem, often expressing praise or strong emotions
Example
The poet wrote an ode to the beauty of nature.
詩人は自然の美に対するオードを書いた。
B1 adjective /əˈfɪʃəl/

official

公式
Meaning
relating to or connected with an authority or public office
Example
He is the official spokesperson for the company.
彼は会社の公式なスポークスマンです。
C2 adjective /əˈrækjələr/

oracular

神託のような
Meaning
Resembling an oracle; giving wise, mysterious, or prophetic statements
Example
Her oracular words left the audience deep in thought.
彼女の神託のような言葉は、観客を深く考えさせた。
C1 noun /ˈaʊtpoʊst/

outpost

前哨基地
Meaning
A small military camp or position at some distance from the main force, used especially as a guard.
Example
The soldiers were stationed at a remote outpost.
兵士たちは遠隔地の前哨基地に配置されました。
C1 noun /ˈoʊ.mən/

Omen

未来の良いまたは悪い運命の兆し
Meaning
an event regarded as a sign of future good or bad luck
Example
Many people consider a black cat crossing your path a bad omen.
多くの人々は、黒猫が道を横切ることを悪いオーメンだと考えています。
C1 adjective /ˌɑːpərˈtuːn/

opportune

適切な瞬間
Meaning
Happening at a suitable or convenient time.
Example
She arrived at an opportune moment to help.
彼女は助けるために適切な瞬間に到着しました。
C2 noun /ˈoʊdiəm/

odium

嫌悪
Meaning
general or widespread hatred or disgust directed toward someone as a result of their actions
Example
The scandal brought public odium on the corrupt minister.
スキャンダルは腐敗した大臣に対する公衆の嫌悪を引き起こした。
A1 adjective /oʊˈkeɪ/

ok

わかった
Meaning
used to indicate agreement, approval, or understanding
Example
Okay, let's go to the park.
わかった、じゃあ公園に行こう。
B2 verb /əˈfend/

offend

侮辱する
Meaning
to cause displeasure or resentment; to hurt someone's feelings
Example
His rude comments offended many people at the meeting.
彼の無礼なコメントは会議で多くの人々を怒らせました。
B1 noun ˌɔː.ɡən.aɪˈzeɪ.ʃənz

organizations

組織
Meaning
Organized groups of people with a particular purpose
Example
Organizations play a key role in policymaking.
組織は政策形成において重要な役割を果たします。
C2 adjective /ˈoʊ.pən ˈhɑrt.ɪd/

Open-hearted

オープンハート; 寛大で誠実; 心温かく受け入れる;
Meaning
Kind and generous; sincere and honest; warmly receptive;
Example
She welcomed the strangers with an open-hearted smile and invited them for dinner.
彼女は見知らぬ人々を心温かい笑顔で迎え、夕食に招待した。
C1 noun /ˈɒstrəsɪzəm/

ostracism

追放
Meaning
The act of excluding someone from a group or society.
Example
The student faced ostracism after breaking the rules.
その学生は規則を破った後、追放に直面しました。
C1 noun /ˈoʊ.vər spɪl/

Over-spill

オーバーフロー
Meaning
the overflow of liquid from a container; excess that cannot be contained
Example
The overspill from the river flooded nearby farms.
川の溢れが近くの農場を水浸しにした。
C2 adjective /ˈoʊ.kən/

oaken

オーク材で作られた
Meaning
made of or resembling oak wood
Example
The villagers gathered around the oaken table in the hall.
村人たちはホールの中のオーク材のテーブルの周りに集まりました。
B2 noun ɔːˈɡæn.ɪk fuːdz

organic foods

オーガニック食品
Meaning
Food produced without the use of chemicals such as artificial pesticides, fertilizers, or other artificial agents.
Example
Organic foods are healthier than processed foods.
オーガニック食品は加工食品よりも健康的です。
B1 verb /ˈɔːrɡənaɪz/

organize

整理する
Meaning
to arrange systematically; to plan and coordinate
Example
She organized a surprise party for her friend.
彼女は友達のためにサプライズパーティーを企画した。
A1 adverb /wʌns/

Once

一度; 過去に
Meaning
one time only; at some time in the past; formerly
Example
I have been to Paris once in my life.
私は一度だけパリに行ったことがあります。
C1 noun /oʊˈbɪt.ʃu.er.i/

Obituary

訃報
Meaning
a notice of someone's death published in a newspaper; biographical account of deceased person
Example
The newspaper published his obituary yesterday.
新聞は昨日彼の訃報を掲載しました。
B2 noun /ˈɔɪ.stər/

Oyster

オイスター
Meaning
a type of shellfish that can be eaten and sometimes contains pearls
Example
She ordered fresh oysters at the seafood restaurant.
彼女はシーフードレストランで新鮮なオイスターを注文しました。
B2 verb /əˈblaɪdʒ/

oblige

義務付ける
Meaning
to compel or require someone to do something; to help or do a favor
Example
I would be happy to oblige you with the information you need.
必要な情報を提供してお手伝いできれば嬉しいです。
A2 pronoun /aʊərˈsɛlvz/

ourselves

私たち自身
Meaning
used by the speaker to refer to themselves and one or more others as the object of the verb
Example
We should help ourselves before helping others.
私たちは他の人を助ける前に、自分たち自身を助けるべきです。
C1 noun /ˈɒktɪv/

octave

Meaning
A series of eight musical notes, or the interval between one musical pitch and another with double its frequency.
Example
The singer's voice could easily reach the higher octave.
C2 noun /ˌoʊpəˈlɛsəns/

opalescence

オパレスセンス
Meaning
a milky or pearly appearance of a surface like that of an opal
Example
The pearl had a gentle opalescence under the light.
パールは光の下で優しいオパレスセンスを持っていました。
C2 noun /ˌɔːrnɪˈθɑːlədʒi/

ornithology

鳥類学
Meaning
the scientific study of birds
Example
She pursued ornithology to understand the migration patterns of birds.
彼女は鳥の移動パターンを理解するためにオルニソロジーを追求しました。
B2 noun /ˈɒfərɪŋ/

offering

オファリング
Meaning
something that is given, especially as a gift or contribution
Example
The company’s latest offering is an eco-friendly car.
会社の最新のオファリングは、エコフレンドリーな車です。
C2 verb /əbˈvɜːrt/

obvert

反転する
Meaning
To turn something so as to face in a different direction; in logic, to convert a proposition by negating both subject and predicate.
Example
The teacher asked the students to obvert the statement for practice.
先生は生徒たちに練習のためにその声明をオブバートするように頼みました。
B2 noun /əˈfens/

Offence

違反; 犯罪
Meaning
a breach of law or rule; an annoyance or resentment
Example
Stealing is a serious offence punishable by law.
窃盗は法律で罰せられる重大な違反です。
C2 noun /ˌɒn.əˌmæt.əˈpiː.ə/

onomatopoeia

オノマトペ
Meaning
The formation of a word from a sound associated with what is named.
Example
The word 'buzz' is an example of onomatopoeia.
'バズ'という言葉はオノマトペの一例です。
A1 adverb /ɔːf/

off

オフ
Meaning
away from a place, position, or time; not functioning
Example
He turned off the light before leaving the room.
彼は部屋を出る前に電気をオフにしました。
C1 noun /əˈfen.dər/

Offender

犯罪者; 法律違反者
Meaning
a person who commits an illegal act; someone who breaks the law
Example
The young offender was sentenced to community service.
その若い犯罪者はコミュニティサービスを命じられました。
A2 adverb; noun /ˌaʊtˈdɔːrz/

outdoors

屋外で
Meaning
outside a building; the natural environment outside
Example
We spent the whole afternoon outdoors enjoying the fresh air.
私たちは午後ずっと屋外で新鮮な空気を楽しみました。
C2 noun /ˈɔːrdnəns/

ordnance

軍需品
Meaning
Military supplies including weapons, ammunition, and combat equipment.
Example
The army stored ordnance in a secure facility outside the city.
軍隊は都市外の安全な施設に軍需品を保管していた。
B2 noun /ˈaʊtˌsɛt/

outset

開始
Meaning
the beginning or start of something
Example
From the outset, the project seemed ambitious but achievable.
最初から、プロジェクトは野心的だが達成可能に見えました。
B1 verb /əbˈzɜːrv/

observe

観察する
Meaning
to watch carefully; to notice or perceive something
Example
Scientists observe the behavior of animals in the wild.
科学者たちは野生動物の行動を観察します。
C1 verb /aʊst/

oust

追放する
Meaning
To remove someone from a position or place of power or authority.
Example
The rebels ousted the dictator from power.
反乱者は独裁者を権力から追い出しました。
B1 adjective /əˈkeɪ.ʒən.əl/

Occasional

偶然の
Meaning
occurring infrequently or irregularly; happening from time to time
Example
She enjoys occasional walks in the park.
彼女は公園で偶然の散歩を楽しんでいます。
B2 verb /ˌoʊvərˈtɜrn/

overturn

覆す / 判決を覆す
Meaning
to turn something upside down or to reverse a decision or judgment
Example
The court decided to overturn the previous ruling.
裁判所は前回の判決を覆すことに決めました。
C2 noun /ɒkˈteɪvoʊ/

octavo

オクターヴォ (紙を8つに折りたたんで作られた本のサイズ)
Meaning
A size of book page resulting from folding a sheet of paper into eight leaves (sixteen pages).
Example
The old library contained rare octavo editions of Shakespeare.
古い図書館にはシェイクスピアの珍しいオクターヴォ版がありました。
B2 adverb /ˈəʊvəli/

overly

過度に
Meaning
to an excessive degree or extent
Example
She was overly concerned about the results.
彼女は結果について過度に心配していた。
C2 noun /ˈɔː.rɪ.fɪs/

orifice

孔
Meaning
an opening or hole, especially in the body or a device
Example
The medicine was applied through a small orifice in the device.
薬は装置の小さな孔から適用されました。
C1 verb /aʊtˈwɪt/

outwit

巧妙に出し抜く
Meaning
to defeat or gain an advantage over someone by being more clever or cunning
Example
The fox managed to outwit the hunters.
キツネは猟師たちを出し抜くことができました。
B2 noun oʊˈbiː.sə.t̬i

obesity

肥満
Meaning
The condition of being grossly fat or overweight.
Example
Obesity increases the risk of diabetes and heart disease.
肥満は糖尿病と心臓病のリスクを高めます。
C1 noun /oʊˈmɪʃ.ən/

Omission

省略; 除外
Meaning
the action of excluding or leaving out someone or something; a failure to include
Example
The omission of his name from the list was intentional.
リストから彼の名前を省略することは意図的でした。
C2 noun ˈɒpjʊləns

opulence

富裕
Meaning
Great wealth or luxuriousness.
Example
The opulence of the mansion was evident in its ornate furnishings.
豪邸の富裕さはその華やかな家具に明らかでした。
C1 noun /ˌɒk.sɪ.dʒɪˈneɪ.ʃən/

oxygenation

酸素供給または治療
Meaning
The process of supplying or treating with oxygen.
Example
Deep breathing exercises improve oxygenation of the body.
深呼吸の練習は身体の酸素供給を改善します。
C1 adjective /ˌaʊt ən ˈaʊt/

out-and-out

完全な
Meaning
complete; absolute; used to emphasize something extreme
Example
The speech was an out-and-out lie.
そのスピーチは完全な嘘だった。
C2 adjective /ˈɒfɪʃ/

offish

無愛想
Meaning
Unfriendly, distant, or reserved in manner.
Example
He seemed offish at the party and avoided most conversations.
彼はパーティーで無愛想に見え、大半の会話を避けていました。
A2 noun /ˈɒbdʒɪkt/

object

物体
Meaning
a thing that can be seen and touched
Example
The table is an object in the room.
テーブルは部屋の中の物体です。
B2 adjective /ˈɔɪl.i/

Oily

油っぽい; 油で覆われた; 脂っこい
Meaning
covered with oil; containing oil; greasy
Example
Her oily skin needs special care.
彼女の油っぽい肌は特別なケアが必要です。