optimize
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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.
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.
B2 noun /ˈɔːrnəmənt/

ornament

Meaning
A decorative object that adds beauty to something.
Example
The Christmas tree was decorated with colorful ornaments.
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.
C2 noun ˈɒpjʊləns

opulence

Meaning
Great wealth or luxuriousness.
Example
The opulence of the mansion was evident in its ornate furnishings.
B1 adverb /əˈrɪdʒɪnəli/

originally

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

only

Meaning
without others; solely
Example
He is the only person who knows the secret.
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 /əˈprəʊ.bri.əm/

opprobrium

Meaning
Harsh criticism or public disgrace.
Example
The scandal brought opprobrium on the politician.
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.
B2 adjective /ˈaʊtˌɡoʊɪŋ/

outgoing

Meaning
Friendly and sociable; inclined to mix with others.
Example
He is an outgoing person who loves meeting new people.
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 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.
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.
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 /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 /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.
B1 verb /əbˈzɜːrv/

observe

Meaning
to watch carefully; to notice or perceive something
Example
Scientists observe the behavior of animals in the wild.
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.
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.
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.
C1 adjective /əbˈsɛsɪv/

obsessive

Meaning
Relating to or characterized by an obsession; thinking about something too much.
Example
He has an obsessive interest in cleanliness.
C2 verb /ˈɑːskjʊleɪt/

osculate

Meaning
To kiss.
Example
They osculated under the mistletoe during the party.
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.
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.
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.
B2 noun /əˈfɛns/

offense

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

overtone

Meaning
A subtle quality, implication, or additional meaning beyond the obvious.
Example
His speech had political overtones that were hard to ignore.
B1 verb অকার্স

occurs

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

Outcast

Meaning
rejected by society; excluded person
Example
He felt like an outcast in his new school.
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 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 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 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 /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.
A2 noun /ˈoʊpənɪŋ/

opening

Meaning
an act or instance of beginning something
Example
The opening of the new store was a huge success.
C2 adjective /ˈɒkjʊlər/

ocular

Meaning
Relating to the eye or vision.
Example
The patient was referred to a specialist for ocular treatment.
C1 verb /aʊtˈwɪt/

outwit

Meaning
to defeat or gain an advantage over someone by being more clever or cunning
Example
The fox managed to outwit the hunters.
C2 adjective /ˌɒbsəˈlɛsnt/

obsolescent

Meaning
Becoming outdated or on the way to becoming obsolete.
Example
The obsolescent technology could not compete with modern devices.
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.
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.
C1 noun /əbˈzɜːvəns/

observance

Meaning
The practice of following a custom, rule, or religious law.
Example
The festival is held in observance of a centuries-old tradition.
A2 adverb; noun /ˌaʊtˈdɔːrz/

outdoors

Meaning
outside a building; the natural environment outside
Example
We spent the whole afternoon outdoors enjoying the fresh air.
A2 adjective /ˈaʊtdɔːr/

outdoor

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

ornate

Meaning
elaborately or highly decorated
Example
The palace hall was filled with ornate furniture and paintings.
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.
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 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.
A2 modal verb /ɔːt/

ought

Meaning
Used to indicate duty, correctness, or moral obligation.
Example
You ought to respect your elders.
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.
C2 verb /ˈɑːbdʒərˌɡeɪt/

objurgate

Meaning
to scold or rebuke severely
Example
The teacher objurgated the student for being dishonest.
C1 adverb /ˈɒp.tɪ.məl.i/

optimally

Meaning
In the most effective or efficient way possible.
Example
Tasks should be allocated optimally for maximum output.
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 /ˈɒptɪməm/

optimum

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

Offensive

Meaning
causing displeasure or resentment; insulting; aggressive
Example
His offensive remarks hurt everyone's feelings.
C2 noun /oʊd/

ode

Meaning
a lyrical poem, often expressing praise or strong emotions
Example
The poet wrote an ode to the beauty of nature.
B2 noun /ˈaʊtlet/

outlet

Meaning
a means by which something is released, expressed, or distributed
Example
Art is a great outlet for emotions.
C2 adjective /əˈprəʊ.bri.əs/

opprobrious

Meaning
Expressing strong criticism or scorn.
Example
He made opprobrious remarks about his opponent.
B2 noun /ˈɒpəreɪtər/

operator

Meaning
a person who operates equipment, a business, or controls something
Example
The machine operator ensured that everything ran smoothly.
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.
C2 adjective /ɑːlˈfæktəri/

olfactory

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

occident

Meaning
The countries of the West, especially Europe and America.
Example
The Occident has a long history of philosophical thought.
A1 preposition, adverb /ˈoʊvər/

over

Meaning
across, on top of, or beyond
Example
The book is lying over the table.
C2 verb /oʊˈpaɪn/

opine

Meaning
to express an opinion or belief
Example
The professor opined that the policy would fail.
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 adjective /ˈəʊ.dər.əs/

Odorous

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

orchestra

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

ownership

Meaning
The act, state, or right of possessing something; legal title to something.
Example
Ownership of resources was crucial.
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.
A2 adjective /ˈɑp.ə.zɪt/

Opposite

Meaning
Contrary; completely different; facing each other; reverse;
Example
They have opposite views on politics but remain good friends.
C2 noun /ˌɔːrnɪˈθɒlədʒɪst/

ornithologist

Meaning
a scientist who studies birds
Example
The ornithologist spent years studying migratory birds.
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.
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 /əˈblaɪdʒɪŋ/

obliging

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

outer

Meaning
situated on or toward the outside; external
Example
The outer layer of the jacket is waterproof.
A2 adverb /ˈɒbviəsli/

obviously

Meaning
in a way that is easily perceived or understood; clearly
Example
Obviously, he didn’t read the instructions.
B2 noun /ˈoʊ.dər/

Odour

Meaning
a distinctive smell, especially an unpleasant one
Example
The odour of fresh bread filled the kitchen.
C2 noun /ɔːrˈθɑːɡrəfi/

orthography

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

opulent

Meaning
Ostentatiously rich, luxurious, or lavish.
Example
They hosted an opulent wedding with gold decorations.
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 /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 adjective /ˌɔːrnəˈmɛntl/

ornamental

Meaning
Serving as decoration; decorative rather than functional.
Example
The garden was filled with ornamental plants.
C1 noun/verb /ˈoʊvərˌhæŋ/

overhang

Meaning
To extend outward and hang over something; a projecting part.
Example
The roof overhang provides shade in the summer.
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 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.
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 /əˈprɛs.ɪv/

Oppressive

Meaning
Harsh and authoritarian; overwhelming; causing distress; tyrannical;
Example
The oppressive heat made it difficult to work outside during the summer.
C2 noun /ˌɔːrnɪˈθɑːlədʒi/

ornithology

Meaning
the scientific study of birds
Example
She pursued ornithology to understand the migration patterns of birds.
B2 adjective /ˈɒp.ʃən.əl/

Optional

Meaning
not compulsory; left to choice
Example
Wearing a tie is optional for this event.
C2 noun /ɔːˈreɪʃən/

oration

Meaning
A formal speech, especially one given on a ceremonial occasion
Example
The president delivered an inspiring oration.
B2 adverb /ˈɒdli/

oddly

Meaning
in a strange or unusual way; unexpectedly
Example
Oddly, he didn’t seem upset by the bad news.
C1 adjective /ˌaʊtˈlændɪʃ/

outlandish

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

orthopedic

Meaning
Relating to the correction of deformities of bones or muscles.
Example
She visited an orthopedic surgeon for her back pain.
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.
C1 adjective /ˌɒbsəˈliːt/

obsolete

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

orthodox

Meaning
conforming to traditional beliefs or practices
Example
He comes from a very orthodox family.
B1 noun /əˈkeɪ.ʒən/

Occasion

Meaning
a particular time or instance of an event; a special celebration
Example
Their wedding was a joyous occasion.
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.
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.
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 adjective /əbˈsiːkwɪəs/

obsequious

Meaning
Excessively obedient or attentive in a servile way.
Example
The waiter gave an obsequious bow to every customer.
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.
B1 verb /əˈkɜːr/

occur

Meaning
to happen or take place; to be found or present
Example
The accident occurred at the intersection during rush hour.
B2 verb /əˈpoʊz/

oppose

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