obsolescence
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C1 noun ˌɒb.səˈlɛs.əns

obsolescence

陳腐化
Meaning
The process of becoming obsolete or outdated and no longer used.
Example
The rapid advancement of technology leads to the obsolescence of old devices.
テクノロジーの急速な進歩は古いデバイスの陳腐化を引き起こします。
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 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。
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。
B2 noun /ˈɒpəreɪtər/

operator

オペレーター
Meaning
a person who operates equipment, a business, or controls something
Example
The machine operator ensured that everything ran smoothly.
機械オペレーターは、すべてがスムーズに動作することを確認しました。
A2 noun /ˈʌn.jən/

Onion

玉ねぎ
Meaning
a round vegetable with a strong taste and smell, made up of many layers
Example
I need to chop some onions for the curry recipe.
カレーのレシピのためにいくつか玉ねぎを切る必要があります。
C2 verb /əˈkluːd/

occlude

閉塞する
Meaning
To block or close up an opening or passage.
Example
The pipe was occluded by mineral deposits.
パイプは鉱物の堆積物で閉塞されていました。
C1 verb /ˈɒs.ɪ.leɪt/

oscillate

二つの点または状態の間で前後に動くまたは揺れる
Meaning
To swing or move back and forth between two points or states
Example
The stock market tends to oscillate during uncertain times.
株式市場は不確実な時期に振動しがちです。
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。
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 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。
C2 adjective /ˌoʊvərˈwiːnɪŋ/

overweening

過度に傲慢な
Meaning
excessively arrogant or prideful
Example
His overweening pride cost him many friends.
彼の過度の誇りは多くの友人を失わせました。
C1 noun /ˈɔr.ə.kəl/

Oracle

オラクル
Meaning
a person regarded as a source of wise counsel; in ancient times, a priest or priestess acting as a medium
Example
The ancient Greeks consulted the oracle at Delphi.
古代ギリシャ人はデルポイのオラクルに相談しました。
C2 noun /ˌɔːrnɪˈθɒlədʒɪst/

ornithologist

鳥類学者
Meaning
a scientist who studies birds
Example
The ornithologist spent years studying migratory birds.
そのオルニソロジストは渡り鳥を研究するために何年も費やしました。
C1 adjective /əˈkʌlt/

occult

オカルト
Meaning
Relating to mysterious, supernatural, or magical powers and practices.
Example
She had always been fascinated by the occult and its hidden knowledge.
彼女は常にオカルトとその隠された知識に魅了されていた。
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.
B2 adverb /ˌoʊvərˈnaɪt/

Overnight

一晩で; 突然; 非常に速く
Meaning
during the night; suddenly; very quickly
Example
The city was transformed overnight.
街は一晩で変わった。
C1 noun /ˈɑːdəsi/

odyssey

長い旅
Meaning
a long, adventurous journey; a series of experiences
Example
Her career has been an odyssey of challenges and achievements.
彼女のキャリアは挑戦と成果の長い旅でした。
B1 adjective /əˈbiː.di.ənt/

Obedient

従順な
Meaning
willing to comply with orders or instructions; submissive
Example
The obedient student always follows the teacher's instructions.
従順な生徒はいつも先生の指示に従う。
B2 adjective /ˈɒp.ʃən.əl/

Optional

任意
Meaning
not compulsory; left to choice
Example
Wearing a tie is optional for this event.
このイベントではネクタイの着用は任意です。
C1 noun /ˈɔːrθədɑːksi/

orthodoxy

正統
Meaning
traditional or generally accepted beliefs and practices
Example
The religious leader defended the orthodoxy of the faith.
宗教指導者は信仰の正統性を守った。
C1 adjective /ˌɒbsəˈliːt/

obsolete

時代遅れ
Meaning
No longer in use or out of date.
Example
Floppy disks are now completely obsolete.
フロッピーディスクは現在完全に時代遅れです。
C1 adjective /ˌɔːrθəˈpiːdɪk/

orthopedic

骨や筋肉の変形の修正に関連する
Meaning
Relating to the correction of deformities of bones or muscles.
Example
She visited an orthopedic surgeon for her back pain.
彼女は背中の痛みのために整形外科医に行った。
C2 noun /ˌɒpəˈrɛtə/

operetta

軽いオペラ
Meaning
a short opera with light and humorous themes
Example
The theater staged a famous operetta by Gilbert and Sullivan.
劇場はギルバートとサリヴァンの有名な軽いオペラを上演しました。
B2 noun /ˈaʊtˌskɜːrt/

outskirt

郊外
Meaning
the outer edge or border of a town or city
Example
They built a new factory on the outskirts of the city.
彼らは街の郊外に新しい工場を建てました。
A1 noun/adjective/adverb /ˌaʊtˈsaɪd/

outside

外
Meaning
the external part or surface of something; beyond the boundary
Example
Children were playing outside in the yard.
子供たちは庭で外で遊んでいました。
B1 noun /ˈɔr.ə.ʒɪn/

Origin

起源
Meaning
the point or place where something begins, arises, or is derived; the source
Example
Scientists are studying the origin of the universe.
科学者たちは宇宙の起源を研究しています。
B2 adjective /ˌoʊvərˈwɛlmɪŋ/

overwhelming

圧倒的
Meaning
Very intense; overpowering.
Example
Large tasks can feel overwhelming.
大きな仕事は圧倒的に感じることがあります。
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。
B2 adjective + noun ˈɒptɪməl ˈtempərətʃər

optimal temperature

最適温度
Meaning
The best or most favorable temperature for a particular purpose
Example
Winter provides optimal temperature for farming.
冬は農業に最適な温度を提供します。
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。
C1 adjective /ˌoʊvərˈrɔt/

overwrought

興奮した / 過度に緊張した
Meaning
extremely agitated or nervous; excessively elaborate
Example
She was too overwrought to speak clearly after the accident.
事故後、彼女は興奮しすぎて、はっきりと話すことができなかった。
B1 noun /ˌɒpəˈreɪʃən/

operation

手術
Meaning
an act or process of functioning or operating
Example
The hospital performed a successful operation.
病院は成功した手術を行いました。
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。
A1 adjective /oʊld/

old

古い
Meaning
having lived for a long time; not new or young
Example
He still drives his old car.
彼は今でも古い車を運転しています。
A2 modal verb /ɔːt/

ought

べき
Meaning
Used to indicate duty, correctness, or moral obligation.
Example
You ought to respect your elders.
あなたは年長者を尊敬すべきです。
A1 preposition /ɒn/

on

上
Meaning
physically in contact with and supported by a surface
Example
The book is on the table.
本はテーブルの上にあります。
B2 verb /ˌoʊvərˈwɛlm/

overwhelm

Meaning
to overpower someone emotionally or physically; to be too much to handle
Example
She was overwhelmed with gratitude after receiving the help.
B1 noun /əˈpɪn.jən/

Opinion

意見
Meaning
a view or judgment formed about something; a belief or assessment based on grounds short of proof
Example
In my opinion, this is the best solution.
私の意見では、これは最良の解決策です。
C2 adjective /ˌoʊpəˈlɛsənt/

opalescent

オパール色の
Meaning
showing or reflecting a milky, iridescent light like an opal
Example
The opalescent sky glowed with shades of pink and blue.
オパレッセントな空はピンクと青の色合いで輝いていた。
C1 verb /ˈɒp.tɪ.maɪz/

optimize

最適化する
Meaning
To make the best or most effective use of a situation, opportunity, or resource.
Example
The company is working to optimize its supply chain.
会社はサプライチェーンの最適化に取り組んでいます。
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 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 /əbˈzɜːrvətɔːri/

observatory

天文台
Meaning
A building equipped for observing astronomical or meteorological events.
Example
The observatory is open to the public on weekends.
天文台は週末に一般公開されています。
C1 noun /ˌəʊvərɪksˌplɔɪˈteɪʃən/

overexploitation

過剰搾取
Meaning
The unsustainable use of natural resources at a rate that exceeds their ability to regenerate, leading to depletion and environmental degradation.
Example
Overexploitation of natural resources leads to environmental degradation.
自然資源の過剰搾取は環境の悪化を引き起こします。
B2 adjective /ˌɔːɡənaɪˈzeɪʃənəl/

organizational

組織的
Meaning
relating to the structure or arrangement of a company or group
Example
He works on improving the organizational structure of the company.
彼は会社の組織構造を改善するために働いています。
B2 noun /ˈaʊt.breɪk/

Out-break

発生
Meaning
a sudden occurrence or eruption of something, especially disease or violence
Example
The outbreak of flu affected many students in the school.
インフルエンザの流行は学校の多くの生徒に影響を与えた。
C2 noun /ˈɔːrɪndʒfɪn ˈleɪbiːoʊ/

Orangefin labeo

オレンジフィンラベオ
Meaning
a freshwater fish species native to South Asian rivers, commonly found in Bangladesh and India
Example
The orangefin labeo is an important food fish in Bangladesh.
オレンジフィンラベオはバングラデシュで重要な食用魚です。
B2 noun /ˌɒpəˈzɪʃən/

opposition

反対
Meaning
the action of opposing or resisting something
Example
The opposition to the new law was strong.
新しい法律に対する反対は強かった。
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。
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。
C2 verb /ˌaʊtməˈnuːvər/

outmaneuver

巧妙に出し抜く
Meaning
to gain an advantage over an opponent by skillful or clever action
Example
The smaller company managed to outmaneuver its larger rival.
小さな会社は大きな競争相手を巧妙に出し抜くことに成功した。
C2 noun /oʊf/

Oaf

不器用で愚かな、無神経な人
Meaning
a clumsy, stupid, or insensitive person
Example
Don't be such an oaf - handle the dishes carefully!
そんなオーフにならないで – お皿は気をつけて洗って！
C1 adjective /əˈprɛs.ɪv/

Oppressive

抑圧的
Meaning
Harsh and authoritarian; overwhelming; causing distress; tyrannical;
Example
The oppressive heat made it difficult to work outside during the summer.
厳しい暑さは夏の間外で働くのを難しくした。
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。
B2 adjective /ˈɒp.tɪ.məl/

optimal

最適、最良
Meaning
Best or most favorable; the most effective under particular conditions.
Example
The optimal temperature for plant growth is around 25°C.
植物の成長に最適な温度は約25°Cです。
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。
C2 verb /ˈɑːbdʒərˌɡeɪt/

objurgate

厳しく叱る
Meaning
to scold or rebuke severely
Example
The teacher objurgated the student for being dishonest.
先生は不正直な生徒を厳しく叱った。
C2 noun /oʊliˈændər/

Oleander

オレアンダー
Meaning
a poisonous evergreen shrub with clusters of white, pink, or red flowers
Example
The beautiful oleander flowers bloomed in the garden despite their toxic nature.
美しいオレアンダーの花が庭で咲いていましたが、その毒性に関わらず。
B2 adjective /ˈaʊtˌɡoʊɪŋ/

outgoing

社交的
Meaning
Friendly and sociable; inclined to mix with others.
Example
He is an outgoing person who loves meeting new people.
彼は新しい人々と会うのが好きな社交的な人です。
B2 noun /ˈɔːrɡənaɪzər/

organizer

主催者
Meaning
a person who arranges or coordinates activities, events, or groups; a tool or item used to keep things in order
Example
She worked as the main organizer of the international conference.
彼女は国際会議の主要な主催者だった。
A2 adjective/adverb /ˈɒnˌlaɪn/

online

オンライン
Meaning
connected to or available through the internet
Example
I prefer shopping online rather than going to stores.
私はお店に行くよりもオンラインで買い物をする方が好きです。
A1 adverb /ˈɔːfən/

often

しばしば
Meaning
frequently, many times
Example
I often visit my grandparents on weekends.
私は週末にしばしば祖父母を訪れます。
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。
C2 noun /ˈɒlɪv brɑːntʃ/

olive-branch

オリーブの枝
Meaning
A symbol of peace or reconciliation; an offer to end conflict.
Example
He extended an olive-branch to his rival after years of hostility.
彼は長年の敵対後、ライバルにオリーブの枝を差し出した。
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 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 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。
C1 verb /ˌoʊvərˈʃædoʊ/

overshadow

覆い隠す
Meaning
to appear more important or significant than something else, reducing its impact
Example
The scandal overshadowed his achievements.
スキャンダルは彼の業績を影にしました。
B1 noun /əˈkeɪ.ʒən/

Occasion

機会; 特別な出来事
Meaning
a particular time or instance of an event; a special celebration
Example
Their wedding was a joyous occasion.
彼らの結婚式は喜ばしい機会でした。
B2 adjective /əˈpəʊzd/

opposed

反対の
Meaning
being against or in disagreement with something
Example
She is strongly opposed to animal testing.
彼女は動物実験に強く反対しています。
C2 adjective /ˌɒbsəˈlɛsnt/

obsolescent

時代遅れの
Meaning
Becoming outdated or on the way to becoming obsolete.
Example
The obsolescent technology could not compete with modern devices.
時代遅れの技術は現代のデバイスには競争できなかった。
A2 verb /oʊˈbeɪ/

obey

従う
Meaning
to follow orders or instructions; to comply with rules
Example
Children should obey their parents and teachers.
子供たちは親と先生に従うべきです。
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 /ˈoʊvərˌhɔːl/

overhaul

完全な改修
Meaning
to examine thoroughly and repair or improve something that is worn or ineffective
Example
The company decided to overhaul its outdated computer system.
会社は古くなったコンピュータシステムのオーバーホールを決定した。
C1 noun /ˈɔːrkɪd/

Orchid

オーキッド
Meaning
a diverse family of flowering plants known for their exotic and often fragrant flowers
Example
The white orchid on the windowsill bloomed for months.
窓辺の白いオーキッドは何ヶ月も咲き続けました。
C1 verb ˈɔː.kɪ.streɪ.tɪd

orchestrated

精巧に組織された
Meaning
Planned or coordinated carefully and deliberately.
Example
The attacks were orchestrated with precision.
攻撃は正確に組織されていた。
C1 verb /ˈɔːstrəˌsaɪz/

ostracize

追放する
Meaning
to exclude someone from a group or society; to banish or shun
Example
After the scandal, he was ostracized by his former colleagues.
スキャンダル後、彼は元同僚に追放された。
B2 noun /oʊˈbiː.di.əns/

Obedience

服従
Meaning
compliance with an order, request, or law; submission to authority
Example
Children should show obedience to their parents.
子供たちは両親に従うべきです。
B1 noun əbˈdʒek.tɪv

objective

目標
Meaning
A thing aimed at or sought; a goal.
Example
The main objective is to test sustainability.
メインオブジェクティブは持続可能性をテストすることです。
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。
C2 verb /aʊtˈraɪd/

outride

追い越す
Meaning
to ride faster, farther, or better than someone else
Example
The young rider managed to outride his competitors in the race.
若いライダーはレースで競技者たちを追い越しました。
A2 adjective /əˈlɪmpɪk/

olympic

オリンピック
Meaning
related to the Olympic Games, a major international sporting event
Example
She trained hard to compete in the Olympic Games.
彼女はオリンピックに出場するために一生懸命トレーニングをしました。
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。
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 noun /əbˈzɜːvər/

observer

観察者
Meaning
a person who watches or notices something
Example
The observer took notes during the meeting.
観察者は会議中にメモを取った。
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 adjective /ˈɑːsɪˌfaɪd/

ossified

骨に変わった、硬直した
Meaning
Turned into bone or become rigid; unwilling to change.
Example
The company had an ossified management structure that resisted innovation.
その会社は、革新に抵抗する硬直した管理構造を持っていました。
C1 adjective /ˌoʊvərˈbloʊn/

overblown

誇張された
Meaning
excessively exaggerated or inflated
Example
The controversy was overblown by the media.
メディアによって論争は誇張されました。
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。
C1 noun /ˈɒktəɡən/

octagon

八角形
Meaning
A polygon with eight sides and eight angles.
Example
The stop sign is shaped like an octagon.
ストップサインは八角形をしています。
C1 adjective əʊˈpeɪk

opaque

不透明, 理解しにくい
Meaning
Not able to be seen through; not transparent; difficult to understand.
Example
The glass was too opaque to see through.
そのガラスは不透明すぎて、透けて見えませんでした。
C1 noun /ˈaʊtˌɡroʊθ/

outgrowth

成長
Meaning
something that grows out of something else; a natural development or result
Example
The new policy was an outgrowth of years of debate.
新しい政策は数年の議論の成長でした。
C1 noun /ˈɔɪntmənt/

ointment

軟膏
Meaning
A smooth, oily substance applied to the skin for healing or soothing.
Example
The doctor prescribed an ointment for the burn on his arm.
医師は彼の腕のやけどのために軟膏を処方しました。
C1 adjective /əbˈtjuːs/

Obtuse

鈍い; 理解が遅い; 愚か
Meaning
annoyingly insensitive or slow to understand; lacking in intelligence or perception
Example
He was being deliberately obtuse about the instructions.
彼は指示に関して意図的に鈍かった。
C2 verb /ˈɔːreɪt/

orate

演説する
Meaning
To speak in a formal, often pompous manner
Example
He began to orate at the ceremony.
彼は式で演説を始めました。
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。
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。
C1 adjective /əbˈstrʌk.tɪv/

Obstructive

妨害的な
Meaning
deliberately creating difficulties or preventing progress; hindering or blocking something
Example
The obstructive policies hindered economic growth.
妨害的な政策は経済成長を阻害した。
B2 adjective /ˈɔː.rəl/

Oral

口頭の; 口に関する
Meaning
spoken rather than written; relating to the mouth
Example
The oral examination will test your speaking skills.
口頭試験はあなたの話す能力をテストします。
C2 adjective /ˈɔːrnəri/

ornery

気難しい
Meaning
bad-tempered and combative; stubborn
Example
The ornery old man refused to leave his chair.
その気難しい老人は椅子を離れようとしませんでした。
B2 verb əbˈzɜːrvd

observed

祝う
Meaning
To celebrate or keep a religious or other festival.
Example
The day is observed annually to raise awareness.
その日は毎年意識を高めるために祝われます。
A1 adjective /ˈʌðər/

other

他の
Meaning
used to refer to something different from the one already mentioned or known
Example
I don't want this one, I will take the other one.
これを欲しくない、他のを取るつもりだ。
C1 noun /ˈaʊtˌkraɪ/

outcry

抗議
Meaning
A strong expression of public anger or disapproval.
Example
The decision sparked an outcry among the citizens.
その決定は市民の間で抗議を引き起こしました。
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。
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。
C1 noun /ˈɒf.sprɪŋ/

offspring

子孫
Meaning
a person's child or children; an animal's young
Example
The bird carefully fed its offspring.
その鳥は注意深く自分の子孫に餌を与えました。
C2 noun /əbˈsɪdiən/

obsidian

オブシディアン (黒いガラスのような火山岩)
Meaning
A hard, dark, glasslike volcanic rock formed by rapid solidification of lava.
Example
The knife was made from sharp obsidian.
ナイフは鋭いオブシディアンで作られていた。
C2 noun /ˈoʊpiət/

opiate

Meaning
a drug containing opium or its derivatives, used to relieve pain or cause sleep
Example
The doctor prescribed an opiate to relieve the patient's pain.
B1 noun /aʊl/

Owl

フクロウ
Meaning
a nocturnal bird of prey with large eyes and a hooked beak
Example
The owl hooted softly in the darkness of the forest.
フクロウは森の暗闇で静かに鳴いた。
B1 adverb /əˈrɪdʒɪnəli/

originally

元々
Meaning
in the beginning, at first
Example
Originally, she wanted to be a doctor.
元々、彼女は医者になりたかった。
B1 noun ˌɒpəˈtjuːnɪtiz

opportunities

チャンス
Meaning
A set of circumstances that makes it possible to do something; chances for advancement or success.
Example
Opportunities for jobs decreased.
仕事のチャンスが減少しました。
C1 verb /ˌaʊtˈduː/

outdo

超える
Meaning
To do better than someone else; to surpass.
Example
She always tries to outdo her classmates in exams.
彼女は試験でクラスメートを常に超えようとします。
C1 noun /ˌɒbstəˈtrɪʃən/

obstetrician

産科医
Meaning
A doctor specializing in pregnancy, childbirth, and women's reproductive health.
Example
The obstetrician monitored the mother’s health throughout the pregnancy.
産科医は妊娠中の母親の健康を監視しました。
C2 verb /ˌoʊvərˈliːp/

overleap

飛び越える
Meaning
To jump over something; to omit or disregard something.
Example
He managed to overleap the fence easily.
彼は簡単にフェンスを飛び越えました。
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。
C2 noun /ˈɒrɪz(ə)n/

orison

祈り
Meaning
a prayer, especially a devout or formal one
Example
He whispered a quiet orison before going to sleep.
寝る前に静かな祈りをささやいた。
A1 pronoun, noun, adjective /wʌn/

one

一
Meaning
the number equivalent to the sum of zero and one; a single person or thing
Example
Only one student answered the question.
ただ一人の学生が質問に答えました。
C2 noun /ˈoʊvərlɔːrd/

overlord

領主
Meaning
A ruler, master, or person of great power and authority over others.
Example
The peasants were forced to pay taxes to their overlord.
農民たちは自分たちの領主に税金を払うよう強制されました。
C1 verb /əbˈsɛs/

obsess

Meaning
To preoccupy or fill the mind of someone continually and to an excessive degree.
Example
She tends to obsess over small details.
C1 adjective ˈɒk.sɪ.də.tɪv

oxidative

酸化に関連する
Meaning
Related to or caused by oxidation, especially cellular damage from free radicals.
Example
Excess stress can lead to oxidative damage in cells.
過度のストレスは細胞に酸化的な損傷を引き起こす可能性があります。