overrun
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C1 verb /ˌoʊvərˈrʌn/

overrun

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

outlive

Meaning
to live longer than someone or something else
Example
She outlived all her siblings.
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.
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 noun ɔːrˈdiːl

ordeal

Meaning
A physical or mental painful experience that must be endured
Example
Surviving the wilderness was a tough ordeal for them.
A1 noun /ɒkˈtoʊbər/

october

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

Obstacle

Meaning
something that blocks or makes progress difficult; a barrier
Example
Bad weather was the main obstacle to our journey.
A1 adverb /ˈɔːfən/

often

Meaning
frequently, many times
Example
I often visit my grandparents on weekends.
C1 adjective /əbˈnɒkʃəs/

Obnoxious

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

outmoded

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No longer in fashion or useful; outdated.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

overshadow

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

overwrought

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

offering

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

objective

Meaning
A thing aimed at or sought; a goal.
Example
The main objective is to test sustainability.
C1 adjective /ˌɒmnɪˈprezənt/

omnipresent

Meaning
(of God) present everywhere at the same time.
Example
Social media has become an omnipresent force in modern society.
C2 adjective /ˈɒpjʊlənt/

opulent

Meaning
Ostentatiously rich, luxurious, or lavish.
Example
They hosted an opulent wedding with gold decorations.
B2 adjective /ˈɒp.tɪ.məl/

optimal

Meaning
Best or most favorable; the most effective under particular conditions.
Example
The optimal temperature for plant growth is around 25°C.
C1 noun /ˌɑːk.sɪˈmɔːr.ɒn/

oxymoron

Meaning
a figure of speech where two contradictory terms are combined
Example
The phrase 'deafening silence' is a classic oxymoron.
B2 noun /ˈaʊtˌsɛt/

outset

Meaning
the beginning or start of something
Example
From the outset, the project seemed ambitious but achievable.
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 /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 ɔːˈɡæn.ɪk fuːdz

organic foods

Meaning
Food produced without the use of chemicals such as artificial pesticides, fertilizers, or other artificial agents.
Example
Organic foods are healthier than processed foods.
B2 noun /ˈɔːkɪstrə/

orchestra

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

obsequy

Meaning
A funeral rite, usually used in plural form obsequies.
Example
The village gathered for the obsequy of their beloved teacher.
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.
C2 verb /ˈɒsɪfaɪ/

ossify

Meaning
to turn into bone or become rigid and inflexible
Example
With age, some tissues tend to ossify.
C1 adjective /ɔːˈneɪt/

ornate

Meaning
elaborately or highly decorated
Example
The palace hall was filled with ornate furniture and paintings.
C1 noun /ˈoʊvərˌsiːər/

overseer

Meaning
a person who supervises work or workers; a manager
Example
The overseer made sure the workers followed safety rules.
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.
B2 verb /ˌoʊvərˈiːt/

overeat

Meaning
To eat more food than the body needs.
Example
She tends to overeat when she is stressed.
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.
C2 noun /ɒmˈnɪpətəns/

omnipotence

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

orthography

Meaning
The conventional spelling system of a language.
Example
English orthography can be confusing for learners.
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 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.
C1 noun /ˈaʊtˌkraɪ/

outcry

Meaning
A strong expression of public anger or disapproval.
Example
The decision sparked an outcry among the citizens.
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 /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.
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.
C2 noun /ˌɔːrnɪˈθɑːlədʒi/

ornithology

Meaning
the scientific study of birds
Example
She pursued ornithology to understand the migration patterns of birds.
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.
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.
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 /ˈɑp.ər.ə.tɪv/

Operative

Meaning
Functioning; in effect; working; active;
Example
The new safety protocols became operative immediately after the accident.
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.
B2 noun /ˌɒb.zəˈveɪ.ʃənz/

observations

Meaning
The action or process of observing something carefully.
Example
Observations of distant galaxies provide new insights.
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 verb /əˈfɪʃieɪt/

officiate

Meaning
To perform official duties, especially in a ceremony or as a referee.
Example
The priest will officiate the wedding ceremony.
B1 verb /ˈɔːrɡənaɪz/

organize

Meaning
to arrange systematically; to plan and coordinate
Example
She organized a surprise party for her friend.
C2 adjective /əˈprəʊ.bri.əs/

opprobrious

Meaning
Expressing strong criticism or scorn.
Example
He made opprobrious remarks about his opponent.
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.
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.
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 /əˈrɪdʒɪneɪt/

originate

Meaning
to come into existence; to begin; to create or produce
Example
The tradition originated in ancient times.
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.
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.
C1 noun /ˈɔr.i.ənt/

Orient

Meaning
the East, especially countries of eastern Asia; to determine one's position or direction
Example
Many spices come from the Orient.
A2 adjective /ˈaʊtdɔːr/

outdoor

Meaning
situated, existing, or done outside a building
Example
We planned an outdoor picnic for the weekend.
C1 verb /ˈɒfsɛt/

offset

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

obsolete

Meaning
No longer in use or out of date.
Example
Floppy disks are now completely obsolete.
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.
C1 adjective /ˌɑːpərˈtuːn/

opportune

Meaning
Happening at a suitable or convenient time.
Example
She arrived at an opportune moment to help.
C2 noun /ˈɒksɪdənt/

occident

Meaning
The countries of the West, especially Europe and America.
Example
The Occident has a long history of philosophical thought.
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 + noun ˈɒptɪməl ˈtempərətʃər

optimal temperature

Meaning
The best or most favorable temperature for a particular purpose
Example
Winter provides optimal temperature for farming.
C1 adjective /ˌɔːrθəˈpiːdɪk/

orthopedic

Meaning
Relating to the correction of deformities of bones or muscles.
Example
She visited an orthopedic surgeon for her back pain.
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.
C2 verb /ˌoʊvərˈliːp/

overleap

Meaning
To jump over something; to omit or disregard something.
Example
He managed to overleap the fence easily.
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.
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 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 /ˈɑːsɪˌfaɪd/

ossified

Meaning
Turned into bone or become rigid; unwilling to change.
Example
The company had an ossified management structure that resisted innovation.
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.
C1 adjective /əbˈstrʌk.tɪv/

Obstructive

Meaning
deliberately creating difficulties or preventing progress; hindering or blocking something
Example
The obstructive policies hindered economic growth.
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.
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 /ˈɒn.rʌʃ/

onrush

Meaning
A sudden powerful forward or downward rush or flow.
Example
The onrush of water swept away the bridge.
A1 verb /ˈoʊpən/

open

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

organism

Meaning
a living thing that has an organized structure and can grow and reproduce
Example
Every organism needs water to survive.
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.
B1 noun /aʊl/

Owl

Meaning
a nocturnal bird of prey with large eyes and a hooked beak
Example
The owl hooted softly in the darkness of the forest.
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.
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 /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.
B2 adverb /ˌoʊvərˈnaɪt/

Overnight

Meaning
during the night; suddenly; very quickly
Example
The city was transformed overnight.
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.
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 /ˈoʊ.vɔɪd/

ovoid

Meaning
egg-shaped; resembling an oval or ellipse
Example
The artist painted an ovoid shape in the center of the canvas.
B2 noun ˈɒksɪdʒən prəˈdʌkʃən

oxygen production

Meaning
The process of generating oxygen through photosynthesis or other means.
Example
Plants are vital for oxygen production and the maintenance of life.
C1 noun /ˌəʊvərɪksˌplɔɪˈteɪʃən/

overexploitation

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.
B1 adjective /əˈfɪʃəl/

official

Meaning
relating to or connected with an authority or public office
Example
He is the official spokesperson for the company.
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.
B1 noun ˌɒpəˈtjuːnɪtiz

opportunities

Meaning
A set of circumstances that makes it possible to do something; chances for advancement or success.
Example
Opportunities for jobs decreased.
C2 adjective /ɒmˈnɪp.ə.tənt/

omnipotent

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

overblown

Meaning
excessively exaggerated or inflated
Example
The controversy was overblown by the media.
C2 adjective /ˈəʊ.dər.əs/

Odorous

Meaning
having a strong smell; fragrant; aromatic
Example
The garden was filled with odorous flowers.
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.
B2 adverb /ˈəʊvəli/

overly

Meaning
to an excessive degree or extent
Example
She was overly concerned about the results.
B2 verb /ˌoʊvərˈpeɪ/

overpay

Meaning
To pay more than is necessary or reasonable.
Example
She realized she had overpaid for the concert tickets.
A2 verb /ˈɔːfər/

offer

Meaning
to present something for acceptance or rejection; to propose
Example
She offered to help with the project.
A2 modal verb /ɔːt/

ought

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