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A1 adverb /ˈɔːfən/

often

Meaning
frequently, many times
Example
I often visit my grandparents on weekends.
C2 noun /ˈɒksɪdənt/

occident

Meaning
The countries of the West, especially Europe and America.
Example
The Occident has a long history of philosophical thought.
C1 adjective /ˈɔːrdɪnəl/

ordinal

Meaning
Relating to the order or position of something in a sequence (first, second, third, etc.).
Example
The ordinal number 'third' indicates position in a sequence.
C1 noun /ˈəʊ.nəs/

onus

Meaning
A duty or responsibility, especially a heavy one.
Example
The onus is on the government to provide relief to the victims.
C2 adjective /ɒmˈnɪp.ə.tənt/

omnipotent

Meaning
Having unlimited power; able to do anything; all-powerful.
Example
In many religions, God is considered omnipotent.
C2 verb ˈɑːb.fə.skeɪt

obfuscate

Meaning
Render obscure, unclear, or unintelligible.
Example
Politicians often obfuscate facts to mislead people.
C2 adjective /əbˈsiːkwɪəs/

obsequious

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

odious

Meaning
extremely unpleasant or repulsive
Example
The dictator was remembered for his odious crimes.
C2 noun /ˈəʊpəs/

opus

Meaning
A creative work, especially a large and important piece of music or art.
Example
The composer considered the symphony his greatest opus.
A2 adjective /ˈɒb.vi.əs/

Obvious

Meaning
easily perceived or understood; clear and apparent to the mind
Example
It was obvious that she was upset about something.
C2 verb /əˈkluːd/

occlude

Meaning
To block or close up an opening or passage.
Example
The pipe was occluded by mineral deposits.
B2 noun /ˈɔr.fən/

Orphan

Meaning
a child whose parents are dead; someone without protective support
Example
The orphan was adopted by a loving family.
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 noun ˌɒk.sɪˈdeɪ.ʃən

oxidation

Meaning
A chemical reaction that involves the combination of a substance with oxygen, often causing deterioration.
Example
Oxidation causes metal surfaces to weaken.
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.
C1 noun /ˈɑd.ɪ.ti/

Oddity

Meaning
something that is strange or unusual; a peculiar trait
Example
His habit of sleeping standing up was considered an oddity.
A1 verb /ˈoʊpən/

open

Meaning
to move something so as to allow access; to begin
Example
Please open the door for me.
C2 adjective /ɑːlˈfæktəri/

olfactory

Meaning
Relating to the sense of smell.
Example
The perfume activated her olfactory nerves immediately.
B2 noun /oʊˈbiː.di.əns/

Obedience

Meaning
compliance with an order, request, or law; submission to authority
Example
Children should show obedience to their parents.
B1 adjective, adverb /ˈoʊvərɔːl/

overall

Meaning
in general or as a whole
Example
Overall, the project has been successful.
B2 noun /ˈɔɪ.stər/

Oyster

Meaning
a type of shellfish that can be eaten and sometimes contains pearls
Example
She ordered fresh oysters at the seafood restaurant.
C1 verb /ˈɔːstrəˌsaɪz/

ostracize

Meaning
to exclude someone from a group or society; to banish or shun
Example
After the scandal, he was ostracized by his former colleagues.
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.
C1 noun /ˈaʊtpoʊst/

outpost

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.
B1 adverb /əˈrɪdʒɪnəli/

originally

Meaning
in the beginning, at first
Example
Originally, she wanted to be a doctor.
A1 adverb /wʌns/

Once

Meaning
one time only; at some time in the past; formerly
Example
I have been to Paris once in my life.
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.
A2 adjective /əˈlɪmpɪk/

olympic

Meaning
related to the Olympic Games, a major international sporting event
Example
She trained hard to compete in the Olympic Games.
A2 verb /oʊˈbeɪ/

obey

Meaning
to follow orders or instructions; to comply with rules
Example
Children should obey their parents and teachers.
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.
C2 noun /oʊˈbleɪʃən/

oblation

Meaning
a religious offering, especially of bread or wine to God
Example
The priest placed the oblation on the altar during the ceremony.
B2 adjective; verb (past participle) /ˈɒkjʊpaɪd/

occupied

Meaning
being in use or taken; filled or lived in; controlled or held by force
Example
The room is occupied, so please wait outside.
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.
B2 noun ˈəʊnəʃɪp

ownership

Meaning
The act, state, or right of possessing something; legal title to something.
Example
Ownership of resources was crucial.
C2 noun /ɒmˈnɪpətəns/

omnipotence

Meaning
The quality of having unlimited power or authority.
Example
Many religions describe God’s omnipotence as absolute.
C2 verb /əbˈvɜːrt/

obvert

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.
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.
C1 noun /ˌɒbstəˈtrɪʃən/

obstetrician

Meaning
A doctor specializing in pregnancy, childbirth, and women's reproductive health.
Example
The obstetrician monitored the mother’s health throughout the pregnancy.
C1 noun /ˈoʊvərˌtʊr/

overture

Meaning
An introduction to something more substantial; a proposal or preliminary action.
Example
The peace overture was welcomed by both nations.
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.
C2 noun /ɒmˈnɪʃəns/

omniscience

Meaning
the state of knowing everything
Example
The novel's narrator has an air of omniscience, revealing every character's thoughts.
C1 adjective /əˈkʌlt/

occult

Meaning
Relating to mysterious, supernatural, or magical powers and practices.
Example
She had always been fascinated by the occult and its hidden knowledge.
C2 noun /ˈɔːrɪndʒfɪn ˈleɪbiːoʊ/

Orangefin labeo

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.
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.
C2 noun /ˈoʊvərlɔːrd/

overlord

Meaning
A ruler, master, or person of great power and authority over others.
Example
The peasants were forced to pay taxes to their overlord.
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.
B2 noun /ˈɒt.ər/

Otter

Meaning
a mammal with webbed feet that lives near water and feeds on fish
Example
The playful otter swam gracefully in the river.
C1 verb /ˈɒs.ɪ.leɪt/

oscillate

Meaning
To swing or move back and forth between two points or states
Example
The stock market tends to oscillate during uncertain times.
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 /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.
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 ˈɔː.bɪt

orbit

Meaning
The curved path of a celestial object around a star, planet, or moon.
Example
The satellite maintains its orbit around Earth.
B1 noun əbˈdʒek.tɪv

objective

Meaning
A thing aimed at or sought; a goal.
Example
The main objective is to test sustainability.
B1 verb অকার্স

occurs

Meaning
Happens or takes place, especially as a result of something.
Example
Snowfall occurs in regions with freezing temperatures.
B2 verb /oʊˈmɪt/

omit

Meaning
to leave out or exclude; to fail to include something
Example
Please don't omit any important details from your report.
C1 noun /ˈoʊ.mən/

Omen

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.
B2 noun /ˈaʊtlet/

outlet

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

oscillation

Meaning
The movement back and forth at a regular speed.
Example
The oscillation of the pendulum controls the clock.
B2 verb /ˌoʊvərˈpeɪ/

overpay

Meaning
To pay more than is necessary or reasonable.
Example
She realized she had overpaid for the concert tickets.
B1 noun /ˈɑː.lɪv/

Olive

Meaning
a small oval fruit with a hard pit, typically green or black, used for eating or making oil
Example
Olive oil is considered one of the healthiest cooking oils available.
C1 noun /ˈaʊtˌɡroʊθ/

outgrowth

Meaning
something that grows out of something else; a natural development or result
Example
The new policy was an outgrowth of years of debate.
C1 noun /ˈɔɪntmənt/

ointment

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.
C1 noun /əˈpreʃ.ən/

Oppression

Meaning
cruel or unjust treatment or exercise of authority; the state of being subject to harsh treatment
Example
The people fought against political oppression.
C2 noun /ˈɒrɪz(ə)n/

orison

Meaning
a prayer, especially a devout or formal one
Example
He whispered a quiet orison before going to sleep.
C2 noun /ˈɔːrdnəns/

ordnance

Meaning
Military supplies including weapons, ammunition, and combat equipment.
Example
The army stored ordnance in a secure facility outside the city.
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.
A1 adjective /oʊld/

old

Meaning
having lived for a long time; not new or young
Example
He still drives his old car.
B2 adverb /ˈaʊtraɪt/

Outright

Meaning
completely; directly; without reservation or concealment
Example
She rejected the proposal outright.
C1 adjective /ˈɒptɪməm/

optimum

Meaning
Most conducive to a favorable outcome; best.
Example
To achieve optimum results, we need to improve efficiency.
B2 adjective /ˈɔː.də.li/

Orderly

Meaning
well-organized; systematic; peaceful
Example
Please keep your desk orderly and clean.
B2 noun /ˈaʊtˌbreɪk/

outbreak

Meaning
a sudden start or occurrence of something unpleasant, like disease or violence
Example
There was an outbreak of flu in the city.
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.
C1 noun /oʊˈmɪʃ.ən/

Omission

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.
B1 adjective /ˈɔːɡənaɪzd/

organized

Meaning
Arranged in a systematic way, especially on a large scale.
Example
An organized approach to work increases productivity and reduces stress.
C1 noun /ˈɒfʃuːt/

offshoot

Meaning
A branch or result that develops from something larger or more important.
Example
The startup was an offshoot of a major tech company.
C1 noun ˌɒp.tɪ.maɪˈzeɪ.ʃən

optimization

Meaning
Improving processes to increase performance and efficiency.
Example
SEO optimization helps websites rank higher on search engines.
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.
B1 noun ˌɔː.ɡən.aɪˈzeɪ.ʃənz

organizations

Meaning
Organized groups of people with a particular purpose
Example
Organizations play a key role in policymaking.
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.
C2 verb /ˈɑːblɪˌɡeɪt/

obligate

Meaning
to bind legally or morally; to compel someone to do something
Example
The contract obligates the company to provide timely service.
B1 verb /oʊ/

owe

Meaning
to be under obligation to pay or repay; to be indebted
Example
I owe my success to my parents' support.
C1 verb /ˌoʊvərˈθroʊ/

overthrow

Meaning
To remove a leader or government from power, often by force.
Example
The rebels planned to overthrow the corrupt regime.
C1 noun /ˈaʊtriːtʃ/

outreach

Meaning
The act of providing services or support to people who might not otherwise have access to them.
Example
The charity launched a new outreach program for the homeless.
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 /ˌɔː.ri.enˈteɪ.ʃən/

orientation

Meaning
the process of becoming familiar with a new situation or environment
Example
The company provides an orientation for all new employees.
C2 noun /ˈɒlɪv bɑːb/

Olive barb

Meaning
A small freshwater fish with olive-colored body and barbels
Example
The olive barb is commonly found in South Asian rivers.
C1 verb əˈblɪt.ə.reɪt

obliterate

Meaning
To destroy utterly; wipe out completely, to erase or remove something completely.
Example
The storm obliterated entire villages.
C2 noun /ˈɒkjʊlɪst/

oculist

Meaning
An old-fashioned term for an eye doctor or ophthalmologist.
Example
The village oculist was known for treating various eye diseases.
C1 adjective ˈɒk.sɪ.də.tɪv

oxidative

Meaning
Related to or caused by oxidation, especially cellular damage from free radicals.
Example
Excess stress can lead to oxidative damage in cells.
C1 adjective /ˈɒptɪk/

optic

Meaning
Relating to the eye or vision.
Example
The optic nerve carries signals from the eye to the brain.
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.
C2 noun /ˈoʊ.kəm/

oakum

Meaning
loose fibers obtained by untwisting old ropes, used for caulking ships
Example
The shipbuilders used oakum to seal the gaps in the wooden planks.
C2 noun /ˈoʊdiəm/

odium

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.
C1 adjective /oʊˈbiːs/

obese

Meaning
Extremely overweight; having an excessive amount of body fat.
Example
The doctor advised the obese patient to adopt a healthier lifestyle.
B2 adjective /əˈpəʊzd/

opposed

Meaning
being against or in disagreement with something
Example
She is strongly opposed to animal testing.
C2 noun /ˈɔː.rɪ.fɪs/

orifice

Meaning
an opening or hole, especially in the body or a device
Example
The medicine was applied through a small orifice in the device.
C1 noun /ˈɒf.sprɪŋ/

offspring

Meaning
a person's child or children; an animal's young
Example
The bird carefully fed its offspring.
C2 adjective /ɔːrˈθɑːɡənl/

orthogonal

Meaning
at right angles; independent or unrelated
Example
In mathematics, two vectors are orthogonal if their dot product is zero.
C1 verb /ˈɒfsɛt/

offset

Meaning
To counterbalance or compensate for something.
Example
The company's losses were offset by gains in other departments.
C1 adjective /əˈblɪɡ.ə.tɔː.ri/

obligatory

Meaning
Required by a legal, moral, or other rule; compulsory.
Example
Wearing a seatbelt is obligatory in most countries.
C1 adjective /ˈɑp.ər.ə.tɪv/

Operative

Meaning
Functioning; in effect; working; active;
Example
The new safety protocols became operative immediately after the accident.
B1 verb /əbˈzɜːrv/

observe

Meaning
to watch carefully; to notice or perceive something
Example
Scientists observe the behavior of animals in the wild.
C2 adjective /əbˈstrɛpərəs/

obstreperous

Meaning
Noisy and difficult to control.
Example
The obstreperous students disrupted the class.
C1 adjective /ˌəʊvərˈstɪmjʊˌleɪtɪd/

overstimulated

Meaning
Excessively excited or aroused, overwhelmed by too much stimulus.
Example
Overstimulated minds can lead to burnout and decreased productivity.
B2 noun /ɔːˈræŋ.ʊˌtæŋ/

Orang-Outang

Meaning
a large arboreal ape with long reddish hair, long arms, and hooked hands and feet, native to Borneo and Sumatra
Example
The orangutan swings gracefully through the forest canopy.
C2 adjective /ˈɒpjʊlənt/

opulent

Meaning
Ostentatiously rich, luxurious, or lavish.
Example
They hosted an opulent wedding with gold decorations.
C1 verb ˈɔːr.kɪ.streɪt

orchestrate

Meaning
To plan or coordinate the elements of (a situation) to produce a desired effect, especially surreptitiously.
Example
He skillfully orchestrated the entire event.
C2 noun /əbˈsɪdiən/

obsidian

Meaning
A hard, dark, glasslike volcanic rock formed by rapid solidification of lava.
Example
The knife was made from sharp obsidian.
B2 noun /əˈfɛns/

offense

Meaning
an illegal act; a crime
Example
The offense was committed in broad daylight.
B2 adjective ˌɒp.ərˈeɪ.ʃən.əl

operational

Meaning
In working order; ready for use.
Example
The space project will be operational by 2025.
A2 noun /ˈɒm.lət/

Omelet

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.
B1 adjective /ˌoʊvərˈsiːz/

overseas

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

outlook

Meaning
a person's general attitude or view; a forecast or prospect
Example
The economic outlook for the year is positive.
C1 noun ˌɒb.səˈlɛs.əns

obsolescence

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.
C1 adjective /aʊtˈmoʊdɪd/

outmoded

Meaning
No longer in fashion or useful; outdated.
Example
That old computer is completely outmoded.
C2 verb /ˈɑːbvieɪt/

obviate

Meaning
To remove a need or difficulty; to prevent or avoid something.
Example
This new system obviates the need for manual data entry.
C2 adjective /əˈrækjələr/

oracular

Meaning
Resembling an oracle; giving wise, mysterious, or prophetic statements
Example
Her oracular words left the audience deep in thought.
A1 verb, adjective /oʊn/

own

Meaning
to possess something; belonging to oneself
Example
She owns a beautiful house in the city.
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.