obstreperous
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C2 adjective /əbˈstrɛpərəs/

obstreperous

Meaning
Noisy and difficult to control.
Example
The obstreperous students disrupted the class.
C2 adjective /ˈəʊ.dər.əs/

Odorous

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

olfaction

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

overreach

Meaning
to go beyond what is proper, acceptable, or achievable; to overextend
Example
The politician overreached by making promises he couldn't keep.
A1 adjective /əʊˈkeɪ/

okay

Meaning
used to express agreement or acceptance
Example
It's okay to leave early today.
C1 noun /oʊθ/

Oath

Meaning
a solemn promise or declaration; a sworn statement
Example
The doctor took an oath to help patients.
B1 adjective /əˈkeɪ.ʒən.əl/

Occasional

Meaning
occurring infrequently or irregularly; happening from time to time
Example
She enjoys occasional walks in the park.
C1 verb /aʊst/

oust

Meaning
To remove someone from a position or place of power or authority.
Example
The rebels ousted the dictator from power.
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.
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.
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.
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 /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 noun əˈblɪv.i.ən

oblivion

Meaning
The state of being unaware or unconscious of what is happening; complete forgetfulness.
Example
His name faded into oblivion over time.
C2 noun /ˈɑːbəlɪsk/

obelisk

Meaning
A tall, four-sided, narrow tapering monument with a pyramid-shaped top.
Example
The ancient Egyptians built obelisks to honor their gods.
C2 noun /ˌɑːpərˈtuːnɪzəm/

opportunism

Meaning
The practice of taking advantage of opportunities regardless of principles or ethics.
Example
His decision was driven by opportunism, not values.
C1 adjective /aʊtˈmoʊdɪd/

outmoded

Meaning
No longer in fashion or useful; outdated.
Example
That old computer is completely outmoded.
C2 noun /ˈɑb.lə.kwi/

Obloquy

Meaning
harsh criticism or verbal abuse; strong public condemnation
Example
The politician faced obloquy after the scandal.
B2 adjective /ˌoʊvərˈwɛlmɪŋ/

overwhelming

Meaning
Very intense; overpowering.
Example
Large tasks can feel overwhelming.
B2 noun /ˈaʊtskɜːrts/

outskirts

Meaning
The outer parts of a town or city, away from the center.
Example
They moved to the outskirts of the city for a quieter life.
B2 adjective ˌɒp.ərˈeɪ.ʃən.əl

operational

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

outlaw

Meaning
as a noun: a person who breaks the law and lives outside its protection; as a verb: to make something illegal
Example
The government decided to outlaw the harmful practice.
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 /ˈɔːrkɪd/

Orchid

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.
C1 noun /ˈoʊvərˌsiːər/

overseer

Meaning
a person who supervises work or workers; a manager
Example
The overseer made sure the workers followed safety rules.
C1 adjective /ɔːˈneɪt/

ornate

Meaning
elaborately or highly decorated
Example
The palace hall was filled with ornate furniture and paintings.
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.
B1 adjective /ˈaʊtər/

outer

Meaning
situated on or toward the outside; external
Example
The outer layer of the jacket is waterproof.
B1 noun /əˈpɪn.jən/

Opinion

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.
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.
B1 verb অকার্স

occurs

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

offense

Meaning
an illegal act; a crime
Example
The offense was committed in broad daylight.
C2 noun /ˈɒbsɪkwiːz/

obsequies

Meaning
Funeral rites or ceremonies.
Example
The obsequies for the late leader drew thousands of mourners.
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.
C1 adjective /ˌaʊtˈlændɪʃ/

outlandish

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

overweening

Meaning
excessively arrogant or prideful
Example
His overweening pride cost him many friends.
C1 verb /ˌoʊvərˈrʌn/

overrun

Meaning
to spread over or occupy completely; to exceed a limit or time
Example
The garden was overrun with weeds.
C1 noun /ˈɔːrdɪnəns/

ordinance

Meaning
An authoritative rule, law, or decree issued by a city, town, or authority.
Example
The city council passed an ordinance banning smoking in public parks.
B2 noun /ˈaʊtbɜːrst/

outburst

Meaning
a sudden release of strong emotion or activity
Example
She had an angry outburst during the meeting.
C1 adjective /ˈɒptɪk/

optic

Meaning
Relating to the eye or vision.
Example
The optic nerve carries signals from the eye to the brain.
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.
B2 noun /ˈɒs.trɪtʃ/

Ostrich

Meaning
a large flightless bird native to Africa with long legs and neck
Example
The ostrich is the world's largest bird.
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.
B2 verb əbˈzɜːrvd

observed

Meaning
To celebrate or keep a religious or other festival.
Example
The day is observed annually to raise awareness.
C1 noun /ˈɒktəɡən/

octagon

Meaning
A polygon with eight sides and eight angles.
Example
The stop sign is shaped like an octagon.
B2 adverb /ˈaʊtraɪt/

Outright

Meaning
completely; directly; without reservation or concealment
Example
She rejected the proposal outright.
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.
B1 verb /ˈɔːrɡənaɪz/

organize

Meaning
to arrange systematically; to plan and coordinate
Example
She organized a surprise party for her friend.
C1 noun /ˈɒn.slɔːt/

onslaught

Meaning
A fierce or destructive attack.
Example
The village faced an onslaught of enemy forces.
A1 pronoun, noun, adjective /wʌn/

one

Meaning
the number equivalent to the sum of zero and one; a single person or thing
Example
Only one student answered the question.
C1 noun /ˌɑːsɪˈleɪʃən/

oscillation

Meaning
The movement back and forth at a regular speed.
Example
The oscillation of the pendulum controls the clock.
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.
A2 adjective/adverb /ˈɒnˌlaɪn/

online

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

obeisance

Meaning
A gesture of respect such as a bow or curtsy.
Example
They bowed in obeisance to the king.
C1 noun /ɒpˈtɒmɪtrɪst/

optometrist

Meaning
A healthcare professional who examines eyes and prescribes corrective lenses.
Example
The optometrist prescribed new glasses for her.
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.
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.
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.
A1 verb /ˈoʊpən/

open

Meaning
to move something so as to allow access; to begin
Example
Please open the door for me.
B2 noun /ˌɒpəˈzɪʃən/

opposition

Meaning
the action of opposing or resisting something
Example
The opposition to the new law was strong.
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.
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.
A2 verb /oʊˈbeɪ/

obey

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

obesity

Meaning
The condition of being grossly fat or overweight.
Example
Obesity increases the risk of diabetes and heart disease.
C2 adjective /ɒˈstɛnsɪv/

ostensive

Meaning
clearly demonstrative or pointing out; explicitly shown
Example
The teacher gave an ostensive example to clarify the concept.
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 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.
B1 adjective /ˌoʊvərˈsiːz/

overseas

Meaning
in or to a foreign country across the sea
Example
He went overseas for higher education.
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.
A1 adjective /oʊld/

old

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

operation

Meaning
an act or process of functioning or operating
Example
The hospital performed a successful operation.
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.
A2 noun /ˈɔr.dər/

Order

Meaning
a command or instruction; the arrangement of things following a particular sequence
Example
The teacher gave an order to sit down quietly.
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.
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 adjective /əˈblaɪdʒɪŋ/

obliging

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

oatmeal

Meaning
A type of porridge made from ground oats, often eaten for breakfast.
Example
She eats a bowl of oatmeal every morning for breakfast.
C1 noun /ˈaʊtˌkraɪ/

outcry

Meaning
A strong expression of public anger or disapproval.
Example
The decision sparked an outcry among the citizens.
C1 adjective /oʊˈvɜːrt/

overt

Meaning
Done or shown openly; not hidden or secret.
Example
There was an overt display of hostility between the rivals.
C2 noun /ˌɔːrdɪˈneɪʃən/

ordination

Meaning
The ceremony of conferring holy orders or official religious authority.
Example
The church held a special service for the ordination of new priests.
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.
B1 noun /ˈɔr.ə.ʒɪn/

Origin

Meaning
the point or place where something begins, arises, or is derived; the source
Example
Scientists are studying the origin of the universe.
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.
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.
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.
B2 noun /ˌoʊ.vɚˈkraʊ.dɪŋ/

overcrowding

Meaning
Excessive crowd or packed condition, having more people or vehicles in a place than the approved capacity.
Example
The subway system suffers from severe overcrowding during peak hours.
A2 noun /ˈʌn.jən/

Onion

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.
C1 adjective /ɒˈstɛnsəbl/

ostensible

Meaning
stated or appearing to be true, but not necessarily so
Example
His ostensible reason for leaving was illness, but many doubted it.
B2 verb /əˈrɪdʒɪneɪt/

originate

Meaning
to come into existence; to begin; to create or produce
Example
The tradition originated in ancient times.
B1 adverb /ˈʌðərwaɪz/

Otherwise

Meaning
in a different way; if not; or else; apart from that
Example
Study hard, otherwise you will fail the exam.
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.
A1 pronoun /ˈʌðərz/

others

Meaning
people or things distinct from the ones already mentioned or known
Example
I like to spend time with others.
B2 noun /ɔːrˈɡæn.ɪk ˈfɑːr.mɪŋ/

organic farming

Meaning
Farming method that avoids synthetic chemicals and fertilizers, using natural methods instead.
Example
Organic farming improves soil health and reduces pollution.
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 /ˈoʊvərpæs/

overpass

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

organizational

Meaning
relating to the structure or arrangement of a company or group
Example
He works on improving the organizational structure of the company.
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 ˈoʊʃən ˌstrætɪfɪˈkeɪʃən

ocean stratification

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

Offence

Meaning
a breach of law or rule; an annoyance or resentment
Example
Stealing is a serious offence punishable by law.
C1 noun /ˈɔr.ə.tər/

Orator

Meaning
a public speaker, especially one who is eloquent or skilled in speaking
Example
The famous orator delivered an inspiring speech.
C2 noun /oʊliˈændər/

Oleander

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.
B2 verb /əˈpoʊz/

oppose

Meaning
to disagree with or resist; to act against
Example
Many citizens oppose the new tax policy.
C1 verb /əbˈstrʌkt/

obstruct

Meaning
to block or hinder progress; to prevent or impede movement
Example
The fallen tree obstructed the road for several hours.
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 adjective /ˈɔːrəˌtʌnd/

orotund

Meaning
full, rich, and clear in sound; pompous in style
Example
The actor's orotund voice filled the theater.
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 adjective /aʊtˈstændɪŋ/

outstanding

Meaning
extremely good or impressive; not yet resolved or paid
Example
She received an award for her outstanding performance.
C1 adjective /ˌaʊtˈspoʊkən/

Outspoken

Meaning
frank; speaking directly
Example
She is known for being outspoken about social issues.
C2 adjective /ˈɒsiəs/

osseous

Meaning
consisting of or turned into bone; bony
Example
The fossil showed osseous structures of the ancient creature.
B2 verb /ˌoʊvərˈlʊk/

overlook

Meaning
to fail to notice or consider something; to have a view from above
Example
It's easy to overlook small details when you're in a hurry.
A1 noun /ɒkˈtoʊbər/

october

Meaning
the tenth month of the year in the Gregorian calendar
Example
The weather becomes cooler in October.