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A1 adjective /oʊˈkeɪ/

ok

Meaning
used to indicate agreement, approval, or understanding
Example
Okay, let's go to the park.
C2 adjective /ˈɑːsɪˌfaɪd/

ossified

Meaning
Turned into bone or become rigid; unwilling to change.
Example
The company had an ossified management structure that resisted innovation.
B1 adjective /əˈbiː.di.ənt/

Obedient

Meaning
willing to comply with orders or instructions; submissive
Example
The obedient student always follows the teacher's instructions.
B1 adjective /əˈkeɪ.ʒən.əl/

Occasional

Meaning
occurring infrequently or irregularly; happening from time to time
Example
She enjoys occasional walks in the park.
B2 noun /ˈaʊt.kʌm/

Outcome

Meaning
the result or consequence of an action or situation; the final product
Example
The outcome of the election surprised everyone.
A1 preposition /ɒn/

on

Meaning
physically in contact with and supported by a surface
Example
The book is on the table.
C1 noun /ˌoʊvərprəˈdʌkʃən/

overproduction

Meaning
The act of producing more of something than is needed or can be consumed.
Example
The economic crisis was caused by the overproduction of goods.
A2 noun /ɔɪl/

Oil

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.
C1 noun ˈoʊʃən əˌsɪdɪfɪˈkeɪʃən

ocean acidification

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.
A2 adverb; noun /ˌaʊtˈdɔːrz/

outdoors

Meaning
outside a building; the natural environment outside
Example
We spent the whole afternoon outdoors enjoying the fresh air.
B2 noun /ˈɒfərɪŋ/

offering

Meaning
something that is given, especially as a gift or contribution
Example
The company’s latest offering is an eco-friendly car.
B1 noun /əˈkeɪ.ʒən/

Occasion

Meaning
a particular time or instance of an event; a special celebration
Example
Their wedding was a joyous occasion.
B2 adjective ˌɒp.ərˈeɪ.ʃən.əl

operational

Meaning
In working order; ready for use.
Example
The space project will be operational by 2025.
B2 adjective, verb /əbˈskjʊr/

obscure

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.
B2 adjective ɔːrˈɡæn.ɪk

organic

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.
C2 adjective /ˈoʊ.pən ˈhæn.dɪd/

Open-handed

Meaning
Generous; liberal; giving freely;
Example
He is very open-handed with his money and always helps those in need.
C2 noun /ˌoʊpəˈlɛsəns/

opalescence

Meaning
a milky or pearly appearance of a surface like that of an opal
Example
The pearl had a gentle opalescence under the light.
A2 noun /ˈɒbdʒɪkt/

object

Meaning
a thing that can be seen and touched
Example
The table is an object in the room.
C2 noun /əbˈstɛtrɪks/

obstetrics

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.
B2 noun /ˈaʊtlet/

outlet

Meaning
a means by which something is released, expressed, or distributed
Example
Art is a great outlet for emotions.
C2 verb /ˈɑːskjʊleɪt/

osculate

Meaning
To kiss.
Example
They osculated under the mistletoe during the party.
C2 noun /ˈɔːrdʒi/

orgy

Meaning
A wild party involving excessive indulgence, especially of a sexual nature.
Example
The novel described a scandalous orgy in a wealthy mansion.
C1 adjective /əbˈtjuːs/

Obtuse

Meaning
annoyingly insensitive or slow to understand; lacking in intelligence or perception
Example
He was being deliberately obtuse about the instructions.
B2 noun /ɒpˈtɪʃən/

optician

Meaning
A person who makes or sells glasses and contact lenses.
Example
The optician adjusted my new glasses to fit better.
B2 noun /ˈɒkjʊpənt/

occupant

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.
B2 verb /ˌoʊvərˈduː/

overdo

Meaning
to do something too much; to exaggerate or carry to excess
Example
Don't overdo the exercise on your first day at the gym.
C1 verb /uːz/

ooze

Meaning
to slowly flow or leak out through small openings or pores
Example
Blood began to ooze from the small cut.
C1 verb /ˌoʊvərˈruːl/

overrule

Meaning
to reject or disallow by exercising one's superior authority; to override a decision
Example
The judge overruled the objection from the defense attorney.
C2 noun /ˈɔːrzmən/

Oarsman

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.
B1 adjective /ˌoʊvərˈweɪt/

overweight

Meaning
heavier than is considered healthy or normal
Example
The doctor advised him to lose weight as he was overweight.
C1 noun /ˈɔr.ə.kəl/

Oracle

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.
C2 verb /əbˈtruːd/

obtrude

Meaning
to force oneself or one's ideas into a situation uninvited or inappropriately
Example
He didn’t want to obtrude into their private conversation.
C2 adjective /ˌɔːfˈkiː/

off-key

Meaning
out of tune; not in accordance with expected standards
Example
The singer was slightly off-key during the performance.
C2 verb /ˈoʊɡəl/

ogle

Meaning
To look at someone with obvious sexual interest.
Example
He kept ogling the models on the runway.
C1 verb /ˌoʊvərˈrʌn/

overrun

Meaning
to spread over or occupy completely; to exceed a limit or time
Example
The garden was overrun with weeds.
A2 adjective/adverb /ˈɒnˌlaɪn/

online

Meaning
connected to or available through the internet
Example
I prefer shopping online rather than going to stores.
C2 adjective /ɑːlˈfæktəri/

olfactory

Meaning
Relating to the sense of smell.
Example
The perfume activated her olfactory nerves immediately.
C2 verb /ˌaʊtməˈnuːvər/

outmaneuver

Meaning
to gain an advantage over an opponent by skillful or clever action
Example
The smaller company managed to outmaneuver its larger rival.
C1 adjective /ˈɒm.ɪ.nəs/

Ominous

Meaning
giving the impression that something bad will happen; threatening; foreboding
Example
The dark clouds looked ominous before the storm.
B2 noun /wʌn θɜːd/

one-third

Meaning
one part of something that is divided into three equal parts
Example
One-third of the class was absent today.
C1 noun /oʊθ/

Oath

Meaning
a solemn promise or declaration; a sworn statement
Example
The doctor took an oath to help patients.
C2 verb /ˈɔːreɪt/

orate

Meaning
To speak in a formal, often pompous manner
Example
He began to orate at the ceremony.
C1 verb /əˈprɛs/

oppress

Meaning
to keep someone down by harsh and unfair use of authority; to suppress
Example
The dictator oppressed the people for decades.
C2 noun /ˌɒktədʒəˈnɛəriən/

octogenarian

Meaning
A person who is between 80 and 89 years old.
Example
The octogenarian still jogs every morning to stay healthy.
C1 noun ˈaʊt.sɔːr.sɪŋ

outsourcing

Meaning
The practice of having certain job functions done outside a company instead of having an in-house department or employee handle them.
Example
Many companies use outsourcing to reduce labor costs.
C1 adjective /əbˈnɒkʃəs/

Obnoxious

Meaning
extremely unpleasant; offensive; annoying
Example
His obnoxious behavior at the party annoyed everyone.
C2 noun /ɑːlˈfækʃən/

olfaction

Meaning
The sense of smell; the process of detecting and perceiving odors.
Example
Dogs have a highly developed sense of olfaction.
C1 noun /ˈɒptɪks/

optics

Meaning
The branch of physics dealing with light and vision.
Example
She studied optics to understand how lenses work.
C2 adjective /əˈfɪʃəs/

officious

Meaning
Excessively eager to offer unwanted help or advice; meddlesome.
Example
The officious guard kept interrupting the visitors with unnecessary instructions.
B2 noun/verb /ˈaʊtreɪdʒ/

outrage

Meaning
A strong feeling of anger and shock; to arouse anger or shock.
Example
The unfair decision caused public outrage.
B2 noun /əˌrɪʒ.əˈnæl.ə.ti/

Originality

Meaning
the quality of being novel or unusual; the ability to think independently and creatively
Example
The artist's work showed great originality and creativity.
B2 verb /əˈrɪdʒɪneɪt/

originate

Meaning
to come into existence; to begin; to create or produce
Example
The tradition originated in ancient times.
C1 adjective /ˌəʊ.vərˈɑː.tʃɪŋ/

overarching

Meaning
Comprehensive or all-embracing; forming an arch over something.
Example
The overarching theme of the book is human resilience.
B1 verb /ˈɒpəreɪtɪŋ/

operating

Meaning
to control or manage the functioning of something
Example
The company has been operating in this market for five years.
C1 verb /ˈɒp.tɪ.maɪz/

optimize

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.
B2 verb /ˌoʊvərˈteɪk/

overtake

Meaning
to catch up with and pass someone or something; to surpass
Example
The runner managed to overtake his competitor in the final lap.
C1 adjective/adverb /ˌɒfˈhænd/

offhand

Meaning
Without previous thought or preparation; casual and sometimes dismissive.
Example
She gave an offhand reply to his serious question.
C1 noun /ˈɔːrθədɑːksi/

orthodoxy

Meaning
traditional or generally accepted beliefs and practices
Example
The religious leader defended the orthodoxy of the faith.
C1 noun /ˈɑːlɪˌɡɑːrki/

oligarchy

Meaning
A small group of people having control of a country, organization, or institution.
Example
The nation was ruled by a wealthy oligarchy that controlled all resources.
C1 adjective /aʊtˈmoʊdɪd/

outmoded

Meaning
No longer in fashion or useful; outdated.
Example
That old computer is completely outmoded.
B2 noun /ˈoʊ.vər ɡroʊθ/

Over growth

Meaning
excessive growth beyond normal size; too much development or expansion
Example
The overgrowth of weeds made the garden look untidy.
B2 adjective /aʊtˈstændɪŋ/

outstanding

Meaning
extremely good or impressive; not yet resolved or paid
Example
She received an award for her outstanding performance.
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.
B2 verb /əˈfend/

offend

Meaning
to cause displeasure or resentment; to hurt someone's feelings
Example
His rude comments offended many people at the meeting.
B2 verb /ˌoʊvərˈpeɪ/

overpay

Meaning
To pay more than is necessary or reasonable.
Example
She realized she had overpaid for the concert tickets.
B2 noun /ˈɔːkɪstrə/

orchestra

Meaning
a large group of musicians playing different instruments together
Example
The orchestra performed beautifully at the concert.
C2 adjective /ˈɒf.biːt/

offbeat

Meaning
Unusual, unconventional, or different from the norm.
Example
She has a very offbeat sense of humor.
B1 noun /ˈɔːfɪsər/

officer

Meaning
a person in a position of authority, especially in law enforcement
Example
The officer gave him a ticket for speeding.
C2 noun /ˈɒn.rʌʃ/

onrush

Meaning
A sudden powerful forward or downward rush or flow.
Example
The onrush of water swept away the bridge.
C2 noun /ˌɒpəˈrɛtə/

operetta

Meaning
a short opera with light and humorous themes
Example
The theater staged a famous operetta by Gilbert and Sullivan.
C2 noun /ˌɒn.əˌmæt.əˈpiː.ə/

onomatopoeia

Meaning
The formation of a word from a sound associated with what is named.
Example
The word 'buzz' is an example of onomatopoeia.
A2 pronoun /aʊərˈsɛlvz/

ourselves

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.
A1 adjective /əʊˈkeɪ/

okay

Meaning
used to express agreement or acceptance
Example
It's okay to leave early today.
A2 verb /ˈɔːfər/

offer

Meaning
to present something for acceptance or rejection; to propose
Example
She offered to help with the project.
C1 verb /ˌaʊtˈweɪ/

outweigh

Meaning
To be more important, valuable, or significant than something else.
Example
The benefits of the new policy outweigh the risks.
A2 noun /əˈlɪmpɪks/

olympics

Meaning
an international sports competition held every four years with athletes from many countries
Example
The Olympics bring athletes from all over the world together.
C1 adjective /ɒmˈnɪv.ər.əs/

Omnivorous

Meaning
eating both plants and animals; feeding on various kinds of food
Example
Bears are omnivorous animals that eat both plants and meat.
C2 noun ˌɒbfəsˈkeɪʃən

obfuscation

Meaning
The action of making something obscure, unclear, or unintelligible.
Example
The obfuscation of the data made it difficult to interpret.
B1 noun /ˈɑb.stə.kəl/

Obstacle

Meaning
something that blocks or makes progress difficult; a barrier
Example
Bad weather was the main obstacle to our journey.
C1 adjective /əbˈdʒek.ʃən.ə.bəl/

Objectionable

Meaning
arousing distaste or opposition; unpleasant or offensive
Example
His objectionable behavior made everyone uncomfortable.
C2 noun /ˌɒstɛnˈteɪʃən/

ostentation

Meaning
excessive display of wealth or knowledge intended to attract admiration or envy
Example
The billionaire’s party was full of ostentation and luxury.
C2 noun /oʊf/

Oaf

Meaning
a clumsy, stupid, or insensitive person
Example
Don't be such an oaf - handle the dishes carefully!
C2 noun /əˈblɪkwɪti/

obliquity

Meaning
Deviation from moral or usual conduct; indirectness or lack of straightforwardness.
Example
The politician was criticized for the obliquity of his answers.
C2 adjective /əbˈsiːkwɪəs/

obsequious

Meaning
Excessively obedient or attentive in a servile way.
Example
The waiter gave an obsequious bow to every customer.
C2 noun /ˌɔːrnɪˈθɑːlədʒi/

ornithology

Meaning
the scientific study of birds
Example
She pursued ornithology to understand the migration patterns of birds.
C2 adjective /ˈɔːrnəri/

ornery

Meaning
bad-tempered and combative; stubborn
Example
The ornery old man refused to leave his chair.
C1 adjective /ˈaʊt.kɑːst/

Outcast

Meaning
rejected by society; excluded person
Example
He felt like an outcast in his new school.
B2 noun /əˈpoʊ.nənt/

Opponent

Meaning
a person who disagrees with or resists a proposal or practice; someone who competes against another
Example
The chess player defeated his strongest opponent.
C1 adjective ˈɒb.stɪ.nət

obstinate

Meaning
Refusing to change one's mind or accept others' advice easily.
Example
He remained obstinate despite the logical arguments.
B1 adjective /ˌoʊvərˈsiːz/

overseas

Meaning
in or to a foreign country across the sea
Example
He went overseas for higher education.
B2 noun ˈəʊnəʃɪp

ownership

Meaning
The act, state, or right of possessing something; legal title to something.
Example
Ownership of resources was crucial.
B2 noun /ˈɑp.tə.mɪst/

Optimist

Meaning
a person who tends to be hopeful and confident about the future; someone who sees the good side of things
Example
As an optimist, she always believed things would improve.
C2 adjective /ˈoʊ.pən ˈhɑrt.ɪd/

Open-hearted

Meaning
Kind and generous; sincere and honest; warmly receptive;
Example
She welcomed the strangers with an open-hearted smile and invited them for dinner.
C1 adjective /ˌaʊtˈlændɪʃ/

outlandish

Meaning
Looking or sounding bizarre or unfamiliar; strange.
Example
He wore an outlandish costume to the festival.
C2 adjective /ˈɒkjʊlər/

ocular

Meaning
Relating to the eye or vision.
Example
The patient was referred to a specialist for ocular treatment.
B2 adjective /ˌoʊvərˈwɛlmɪŋ/

overwhelming

Meaning
Very intense; overpowering.
Example
Large tasks can feel overwhelming.
C1 adjective /ˈəʊnərəs/

onerous

Meaning
involving a great deal of effort, difficulty, or burden
Example
Fulfilling the contract proved to be an onerous task for the company.
A1 adverb /aʊt/

out

Meaning
moving or appearing away from the inside or center; not at home or present
Example
He stepped out of the room quietly.
B2 verb /əˈblaɪdʒ/

oblige

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.
C1 noun /əbˈdʒɛktər/

objector

Meaning
a person who expresses opposition or disapproval to something
Example
The objector raised his concerns during the town meeting.
B1 noun /ˌɒp.əˈtjuː.nə.ti/

opportunity

Meaning
A favorable chance or set of circumstances that makes it possible to do something.
Example
She seized the opportunity to study abroad.
B2 noun /ˈɔːrnəmənt/

ornament

Meaning
A decorative object that adds beauty to something.
Example
The Christmas tree was decorated with colorful ornaments.
C2 adjective /ɒmˈnɪp.ə.tənt/

omnipotent

Meaning
Having unlimited power; able to do anything; all-powerful.
Example
In many religions, God is considered omnipotent.
B2 adverb /ˈoʊpənli/

Openly

Meaning
in a frank and honest way; without concealment; publicly
Example
She spoke openly about her struggles with mental health.
B1 noun /ˈɑp.ʃən/

Option

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.
C1 verb /ˌoʊvərˈʃædoʊ/

overshadow

Meaning
to appear more important or significant than something else, reducing its impact
Example
The scandal overshadowed his achievements.
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 /oʊˈpaɪn/

opine

Meaning
to express an opinion or belief
Example
The professor opined that the policy would fail.
B2 adjective /aʊtˈreɪdʒəs/

outrageous

Meaning
Shockingly bad or excessive; very unusual or amusing.
Example
The comedian told an outrageous joke.
C2 adjective /əbˈtruːsɪv/

obtrusive

Meaning
noticeable in an unpleasant or unwelcome way; intrusive
Example
The advertisement was so obtrusive that it ruined the user’s experience.
C2 adjective /ˈɑːbdjʊrət/

obdurate

Meaning
Stubbornly refusing to change one's opinion or course of action.
Example
He remained obdurate despite everyone's pleas.
C1 verb /ˈoʊvərˌhɔːl/

overhaul

Meaning
to examine thoroughly and repair or improve something that is worn or ineffective
Example
The company decided to overhaul its outdated computer system.
B2 noun /oʊk/

oak

Meaning
a large tree that produces acorns and has strong, hard wood
Example
The old oak tree provided shade for the entire yard.
A2 noun /ˈɒpərə/

opera

Meaning
a dramatic performance in which the actors sing most of their lines
Example
We watched a beautiful opera at the theater last night.
C1 noun /ˈɔːr.ə.tɔːr.i/

oratory

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.
B2 noun /ˈɔːrɡənaɪzər/

organizer

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.
A2 verb /oʊˈbeɪ/

obey

Meaning
to follow orders or instructions; to comply with rules
Example
Children should obey their parents and teachers.
B2 verb /əˈpoʊz/

oppose

Meaning
to disagree with or resist; to act against
Example
Many citizens oppose the new tax policy.
B2 adjective /əˈfen.sɪv/

Offensive

Meaning
causing displeasure or resentment; insulting; aggressive
Example
His offensive remarks hurt everyone's feelings.
C1 adjective /ˌoʊvərˈrɔt/

overwrought

Meaning
extremely agitated or nervous; excessively elaborate
Example
She was too overwrought to speak clearly after the accident.
B2 noun /ˌɑb.lɪˈɡeɪ.ʃən/

Obligation

Meaning
a duty or commitment; something that must be done legally or morally
Example
Parents have an obligation to care for their children.