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C1 adjective /ˌɒbsəˈliːt/

obsolete

Meaning
No longer in use or out of date.
Example
Floppy disks are now completely obsolete.
C2 adjective /ˈɑːbdjʊrət/

obdurate

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

obstreperous

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

overwrought

Meaning
extremely agitated or nervous; excessively elaborate
Example
She was too overwrought to speak clearly after the accident.
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 /ˈɒf.sprɪŋ/

offspring

Meaning
a person's child or children; an animal's young
Example
The bird carefully fed its offspring.
B1 verb অকার্স

occurs

Meaning
Happens or takes place, especially as a result of something.
Example
Snowfall occurs in regions with freezing temperatures.
C1 adjective ˈɒptɪmaɪzd

optimized

Meaning
Made as fully perfect, functional, or effective as possible; improved to achieve maximum efficiency.
Example
The system has been optimized for faster performance.
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.
B2 noun /ɒdz/

odds

Meaning
the likelihood or probability of something happening; chances for or against something
Example
The odds of winning the lottery are very low.
A1 adjective /ˈɔːr.ɪndʒ/

Orange

Meaning
having a color between red and yellow like that of a ripe orange fruit
Example
The orange sunset painted the sky magnificently.
C2 noun /ɒmˈnɪpətəns/

omnipotence

Meaning
The quality of having unlimited power or authority.
Example
Many religions describe God’s omnipotence as absolute.
C1 verb /ˌoʊvərˈpaʊər/

overpower

Meaning
To defeat or gain control over someone or something by using greater strength or force.
Example
The soldiers managed to overpower the enemy forces.
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.
C2 noun /ˈɒfərtɔːri/

offertory

Meaning
The part of a religious service when offerings are collected; the offering itself.
Example
The offertory was taken during the Sunday service.
B1 noun ˌɔː.ɡən.aɪˈzeɪ.ʃənz

organizations

Meaning
Organized groups of people with a particular purpose
Example
Organizations play a key role in policymaking.
B1 adjective /ˌoʊld ˈfæʃənd/

old-fashioned

Meaning
not modern; belonging to an earlier time
Example
He still wears an old-fashioned hat.
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.
C1 adjective /əˈblaɪdʒɪŋ/

obliging

Meaning
Willing to help or do favors; accommodating.
Example
The staff at the hotel were very obliging and friendly.
B1 adjective /ˌoʊvərˈsiːz/

overseas

Meaning
in or to a foreign country across the sea
Example
He went overseas for higher education.
C2 noun /ˈɔːfəl/

offal

Meaning
the internal organs and entrails of an animal used as food; waste parts
Example
The butcher prepared sausages using pork offal.
B2 adverb /əˈfɪʃəli/

officially

Meaning
in a formal or authorized way
Example
The building was officially opened by the mayor.
C1 noun /oʊˈbɪt.ʃu.er.i/

Obituary

Meaning
a notice of someone's death published in a newspaper; biographical account of deceased person
Example
The newspaper published his obituary yesterday.
C1 noun /ɔːr/

Oar

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.
C1 adjective /oʊˈvɜːrt/

overt

Meaning
Done or shown openly; not hidden or secret.
Example
There was an overt display of hostility between the rivals.
B2 verb /ɒpt/

opt

Meaning
to choose or decide to do something instead of something else
Example
Many students opt to study abroad for better opportunities.
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.
B2 noun /ˈaʊtˌskɜːrt/

outskirt

Meaning
the outer edge or border of a town or city
Example
They built a new factory on the outskirts of the city.
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 /ˈɒptɪməm/

optimum

Meaning
Most conducive to a favorable outcome; best.
Example
To achieve optimum results, we need to improve efficiency.
A2 noun /ˈoʊ.nər/

Owner

Meaning
a person who owns something; someone who has legal possession of property
Example
The owner of the restaurant greeted us warmly.
B2 adjective /aʊtˈreɪdʒəs/

outrageous

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

overweening

Meaning
excessively arrogant or prideful
Example
His overweening pride cost him many friends.
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 adjective /ˌɔː.riˈen.təl/

Oriental

Meaning
relating to the countries of East Asia; eastern
Example
The museum has a beautiful collection of oriental art.
C2 noun /ˈaʊtˌrɪɡər/

outrigger

Meaning
a projecting structure on a boat, used for stability, or a boat fitted with such support
Example
The fisherman paddled his outrigger canoe across the lagoon.
C1 noun /ˈɑːdəsi/

odyssey

Meaning
a long, adventurous journey; a series of experiences
Example
Her career has been an odyssey of challenges and achievements.
C2 adjective /əˈrækjələr/

oracular

Meaning
Resembling an oracle; giving wise, mysterious, or prophetic statements
Example
Her oracular words left the audience deep in thought.
C1 verb /ˈɒfsɛt/

offset

Meaning
To counterbalance or compensate for something.
Example
The company's losses were offset by gains in other departments.
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.
C2 adjective /ˈoʊ.kən/

oaken

Meaning
made of or resembling oak wood
Example
The villagers gathered around the oaken table in the hall.
C1 noun /ˌɑːpərˈtuːnɪst/

opportunist

Meaning
A person who takes advantage of situations for personal gain, often disregarding principles.
Example
He is seen as an opportunist who always puts his interests first.
B1 noun ˌɔː.ɡən.aɪˈzeɪ.ʃən

organization

Meaning
An organized group of people with a particular purpose, such as a business or government department.
Example
The organization was officially inaugurated in 2024.
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.
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.
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.
C2 noun /ˈɒlɪv brɑːntʃ/

olive-branch

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.
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.
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.
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.
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.
C1 noun ˌoʊ.vɚˈɡreɪ.zɪŋ

overgrazing

Meaning
The practice of allowing livestock to graze to the point of damaging vegetation.
Example
Overgrazing leads to soil erosion and loss of biodiversity.
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 /ˈɔːrnəmənt/

ornament

Meaning
A decorative object that adds beauty to something.
Example
The Christmas tree was decorated with colorful ornaments.
B2 noun /ˈaʊt.laɪn/

Outline

Meaning
a general description or plan showing the essential features of something; the main points
Example
The teacher provided an outline of the course syllabus.
C1 adjective /ˈɒptɪkəl/

optical

Meaning
related to or used in seeing or sight
Example
The optical illusion fooled everyone at the exhibition.
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.
B2 adjective /aʊtˈstændɪŋ/

outstanding

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

overwhelming

Meaning
Very intense; overpowering.
Example
Large tasks can feel overwhelming.
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.
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 verb /ˌoʊvərˈθroʊ/

overthrow

Meaning
To remove a leader or government from power, often by force.
Example
The rebels planned to overthrow the corrupt regime.
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.
A2 modal verb /ɔːt/

ought

Meaning
Used to indicate duty, correctness, or moral obligation.
Example
You ought to respect your elders.
B2 noun /ˈoʊvərpæs/

overpass

Meaning
A bridge that carries one road or railway over another.
Example
The new overpass reduced traffic congestion in the city.
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.
B2 noun /ˌɒb.zəˈveɪ.ʃənz/

observations

Meaning
The action or process of observing something carefully.
Example
Observations of distant galaxies provide new insights.
B2 adverb /ˌoʊvərˈnaɪt/

Overnight

Meaning
during the night; suddenly; very quickly
Example
The city was transformed overnight.
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.
C2 noun /ˈɒbsɪkwiːz/

obsequies

Meaning
Funeral rites or ceremonies.
Example
The obsequies for the late leader drew thousands of mourners.
B2 verb /əbˈteɪn/

obtain

Meaning
to get or acquire something
Example
You need to obtain a visa before traveling abroad.
C2 noun /ɔːrˈθɑːɡrəfi/

orthography

Meaning
The conventional spelling system of a language.
Example
English orthography can be confusing for learners.
C2 adjective /ˈəʊ.dər.əs/

Odorous

Meaning
having a strong smell; fragrant; aromatic
Example
The garden was filled with odorous flowers.
C2 adjective /ɑːlˈfæktəri/

olfactory

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

opine

Meaning
to express an opinion or belief
Example
The professor opined that the policy would fail.
C2 noun /ˈɒb.stɪ.nə.si/

obstinacy

Meaning
Stubborn refusal to change one's opinion or chosen course of action, despite attempts to persuade one to do so.
Example
His obstinacy made negotiations difficult.
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 verb /ˈɒkjʊpaɪ/

occupy

Meaning
to take up space or time; to live or work in a place
Example
The new family will occupy the house next month.
B2 noun /ˈaʊtɪŋ/

outing

Meaning
a short trip or excursion, often for leisure or enjoyment
Example
They had a lovely outing at the beach last weekend.
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 adjective /ɒmˈnɪʃ.ənt/

Omniscient

Meaning
having complete knowledge; all-knowing
Example
The narrator in the novel appears to be omniscient, knowing 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.
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 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.
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.
C1 noun /ˈɒstrəsɪzəm/

ostracism

Meaning
The act of excluding someone from a group or society.
Example
The student faced ostracism after breaking the rules.
C2 adjective /ɒˈstɛnsɪv/

ostensive

Meaning
clearly demonstrative or pointing out; explicitly shown
Example
The teacher gave an ostensive example to clarify the concept.
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 /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.
A1 noun/adjective/adverb /ˌaʊtˈsaɪd/

outside

Meaning
the external part or surface of something; beyond the boundary
Example
Children were playing outside in the yard.
C1 noun /əˈkɜr.əns/

Occurrence

Meaning
an instance or event of something happening; the fact of occurring
Example
The occurrence of earthquakes is common in this region.
A2 noun /ˈoʊpənɪŋ/

opening

Meaning
an act or instance of beginning something
Example
The opening of the new store was a huge success.
A2 verb /oʊˈbeɪ/

obey

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

organ

Meaning
a part of the body that performs a specific function
Example
The heart is an important organ in the human body.
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.
C2 verb /ˌoʊvərˈstraɪd/

overstride

Meaning
To stride over something; to step across with long steps.
Example
He managed to overstride the narrow stream with ease.
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.
C2 noun /əˈprəʊ.bri.əm/

opprobrium

Meaning
Harsh criticism or public disgrace.
Example
The scandal brought opprobrium on the politician.
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.
A1 preposition, adverb /ˈoʊvər/

over

Meaning
across, on top of, or beyond
Example
The book is lying over the table.
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 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.
A2 adjective /ɒd/

Odd

Meaning
strange; unusual; different from what is normal or expected
Example
That's an odd way to solve the problem.
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 noun /əˈfen.dər/

Offender

Meaning
a person who commits an illegal act; someone who breaks the law
Example
The young offender was sentenced to community service.
C1 adjective əʊˈpeɪk

opaque

Meaning
Not able to be seen through; not transparent; difficult to understand.
Example
The glass was too opaque to see through.
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.
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.
C2 noun /ˈɔɪl.mən/

Oilman

Meaning
a person who works in the oil industry; someone who sells oil or petroleum products
Example
The oilman discovered a new oil field in the desert.
B2 noun ˈoʊzoʊn dɪˈpliʃən

ozone depletion

Meaning
The reduction in the amount of ozone in the Earth's stratosphere, leading to increased UV radiation.
Example
Ozone depletion increases UV radiation.
B2 noun /ˈaʊt.breɪk/

Out-break

Meaning
a sudden occurrence or eruption of something, especially disease or violence
Example
The outbreak of flu affected many students in the school.
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 ˈoʊʃən ˌstrætɪfɪˈkeɪʃən

ocean stratification

Meaning
The formation of layers in ocean water due to differences in density.
Example
Ocean stratification affects marine biodiversity.
B2 verb /ˌoʊvərˈloʊd/

overload

Meaning
to load with too much weight or cargo; to give too much work or information
Example
Don't overload the washing machine or it might break down.
C2 noun /ˈɒn.rʌʃ/

onrush

Meaning
A sudden powerful forward or downward rush or flow.
Example
The onrush of water swept away the bridge.
C1 adjective /əbˈstrʌk.tɪv/

Obstructive

Meaning
deliberately creating difficulties or preventing progress; hindering or blocking something
Example
The obstructive policies hindered economic growth.
A2 noun /ˈʌv.ən/

Oven

Meaning
an enclosed compartment used for heating, baking, or drying food
Example
She baked cookies in the oven for thirty minutes.
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.
C1 adjective /ˈɔːrθədɑːks/

orthodox

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