Oracle
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C1 noun /ˈɔr.ə.kəl/

Oracle

Meaning
a person regarded as a source of wise counsel; in ancient times, a priest or priestess acting as a medium
Example
The ancient Greeks consulted the oracle at Delphi.
C2 adjective /ɔːrˈθɑːɡənl/

orthogonal

Meaning
at right angles; independent or unrelated
Example
In mathematics, two vectors are orthogonal if their dot product is zero.
B2 noun ˈaʊt.pʊt

output

Meaning
The amount of something produced by a person, machine, or industry.
Example
Climate change reduces agricultural output.
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.
C2 adjective /ɒˈstɛnsɪv/

ostensive

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

opportune

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

ornithologist

Meaning
a scientist who studies birds
Example
The ornithologist spent years studying migratory birds.
C1 adjective /əbˈnɒkʃəs/

Obnoxious

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

officer

Meaning
a person in a position of authority, especially in law enforcement
Example
The officer gave him a ticket for speeding.
B1 noun /əˈkeɪ.ʒən/

Occasion

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

operator

Meaning
a person who operates equipment, a business, or controls something
Example
The machine operator ensured that everything ran smoothly.
A1 preposition /ʌv/

of

Meaning
expressing the relationship between a part and a whole
Example
The book is on the table, in front of the window.
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.
C2 adjective /ɒmˈnɪp.ə.tənt/

omnipotent

Meaning
Having unlimited power; able to do anything; all-powerful.
Example
In many religions, God is considered omnipotent.
B2 adverb /ˈoʊpənli/

Openly

Meaning
in a frank and honest way; without concealment; publicly
Example
She spoke openly about her struggles with mental health.
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.
B2 noun /ˈaʊtlet/

outlet

Meaning
a means by which something is released, expressed, or distributed
Example
Art is a great outlet for emotions.
A1 pronoun /aʊərz/

ours

Meaning
belonging to or associated with us
Example
This victory is ours.
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.
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.
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.
A2 adjective /ˈɔː.dɪ.nər.i/

Ordinary

Meaning
normal; usual; not special
Example
It was just an ordinary day at the office.
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.
C2 adjective /əˈrækjələr/

oracular

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

out-and-out

Meaning
complete; absolute; used to emphasize something extreme
Example
The speech was an out-and-out lie.
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.
C1 adverb /ˈaʊtwədli/

Outwardly

Meaning
on the surface; externally; in appearance
Example
Outwardly, he seemed calm, but inside he was nervous.
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.
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 /ɒpˈtɪʃən/

optician

Meaning
A person who makes or sells glasses and contact lenses.
Example
The optician adjusted my new glasses to fit better.
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 adverb /ˈɒbviəsli/

obviously

Meaning
in a way that is easily perceived or understood; clearly
Example
Obviously, he didn’t read the instructions.
C1 noun /ˈɒstrəsɪzəm/

ostracism

Meaning
The act of excluding someone from a group or society.
Example
The student faced ostracism after breaking the rules.
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.
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.
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.
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.
C2 noun /ˌɒn.əˌmæt.əˈpiː.ə/

onomatopoeia

Meaning
The formation of a word from a sound associated with what is named.
Example
The word 'buzz' is an example of onomatopoeia.
A1 verb /ˈoʊpən/

open

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

Offence

Meaning
a breach of law or rule; an annoyance or resentment
Example
Stealing is a serious offence punishable by law.
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 verb, adjective /oʊn/

own

Meaning
to possess something; belonging to oneself
Example
She owns a beautiful house in the city.
C2 verb /oʊˈpaɪn/

opine

Meaning
to express an opinion or belief
Example
The professor opined that the policy would fail.
C1 noun ˈaʊt.sɔːr.sɪŋ

outsourcing

Meaning
The practice of having certain job functions done outside a company instead of having an in-house department or employee handle them.
Example
Many companies use outsourcing to reduce labor costs.
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.
B1 adjective /əˈfɪʃəl/

official

Meaning
relating to or connected with an authority or public office
Example
He is the official spokesperson for the company.
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.
C2 verb /ˈɔːreɪt/

orate

Meaning
To speak in a formal, often pompous manner
Example
He began to orate at the ceremony.
B2 noun /ˈɔːkɪstrə/

orchestra

Meaning
a large group of musicians playing different instruments together
Example
The orchestra performed beautifully at the concert.
A1 adverb /ɔːf/

off

Meaning
away from a place, position, or time; not functioning
Example
He turned off the light before leaving the room.
C1 adjective /əˈblaɪdʒɪŋ/

obliging

Meaning
Willing to help or do favors; accommodating.
Example
The staff at the hotel were very obliging and friendly.
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.
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.
A2 noun /ɔɪl/

Oil

Meaning
a viscous liquid derived from petroleum or plants, used for cooking or fuel
Example
Heat the oil in a pan before adding the vegetables.
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.
B2 verb /ˌoʊvərˈsiː/

oversee

Meaning
to supervise or watch over something; to manage and direct
Example
The manager will oversee the entire construction project.
B1 adjective /əˈrɪdʒ.ɪ.nəl/

Original

Meaning
first; fundamental; primary; authentic
Example
This is the original document, not a copy.
C2 adjective /əbˈsiːkwɪəs/

obsequious

Meaning
Excessively obedient or attentive in a servile way.
Example
The waiter gave an obsequious bow to every customer.
B2 noun /ˌɒpəˈzɪʃən/

opposition

Meaning
the action of opposing or resisting something
Example
The opposition to the new law was strong.
B2 adjective /əˈpəʊzd/

opposed

Meaning
being against or in disagreement with something
Example
She is strongly opposed to animal testing.
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.
A2 verb /oʊˈbeɪ/

obey

Meaning
to follow orders or instructions; to comply with rules
Example
Children should obey their parents and teachers.
A1 preposition /ɒn/

on

Meaning
physically in contact with and supported by a surface
Example
The book is on the table.
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.
A2 adjective/adverb /ˈɒnˌlaɪn/

online

Meaning
connected to or available through the internet
Example
I prefer shopping online rather than going to stores.
B2 noun /ˈɔr.fən.ɪʒ/

Orphanage

Meaning
an institution for the care and education of children who have lost their parents
Example
The charity built a new orphanage for homeless children.
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.
B1 adverb /əˈrɪdʒɪnəli/

originally

Meaning
in the beginning, at first
Example
Originally, she wanted to be a doctor.
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 noun /ˌɒpəˈreɪʃən/

operation

Meaning
an act or process of functioning or operating
Example
The hospital performed a successful operation.
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.
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 verb ˈɔː.kɪ.streɪ.tɪd

orchestrated

Meaning
Planned or coordinated carefully and deliberately.
Example
The attacks were orchestrated with precision.
C2 verb /ˌoʊvərˈliːp/

overleap

Meaning
To jump over something; to omit or disregard something.
Example
He managed to overleap the fence easily.
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 noun /ˌɒp.əˈtjuː.nə.ti/

opportunity

Meaning
A favorable chance or set of circumstances that makes it possible to do something.
Example
She seized the opportunity to study abroad.
C2 adjective /ˌoʊvərˈwiːnɪŋ/

overweening

Meaning
excessively arrogant or prideful
Example
His overweening pride cost him many friends.
B2 noun /ˈɒp.tɪ.mɪ.zəm/

optimism

Meaning
Hopefulness and confidence about the future or the successful outcome of something.
Example
Her optimism helped her overcome difficult times.
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 /ˈoʊ.vər spɪl/

Over-spill

Meaning
the overflow of liquid from a container; excess that cannot be contained
Example
The overspill from the river flooded nearby farms.
C1 adjective /ˌɒbsəˈliːt/

obsolete

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

Ominous

Meaning
giving the impression that something bad will happen; threatening; foreboding
Example
The dark clouds looked ominous before the storm.
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.
A2 adverb; noun /ˌaʊtˈdɔːrz/

outdoors

Meaning
outside a building; the natural environment outside
Example
We spent the whole afternoon outdoors enjoying the fresh air.
C1 verb /ˌaʊtˈstrɪp/

outstrip

Meaning
To go faster or do better than someone or something; to surpass.
Example
The company outstripped its competitors in sales last year.
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.
B2 verb /ˌoʊvərˈiːt/

overeat

Meaning
To eat more food than the body needs.
Example
She tends to overeat when she is stressed.
C1 noun /ˈaʊtˌkraɪ/

outcry

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

Overlet

Meaning
a thin mattress or pad placed over a bed for additional comfort
Example
The overlet makes the bed more comfortable to sleep on.
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.
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.
C1 noun /oʊθ/

Oath

Meaning
a solemn promise or declaration; a sworn statement
Example
The doctor took an oath to help patients.
C1 noun /ˈɔːrθədɑːksi/

orthodoxy

Meaning
traditional or generally accepted beliefs and practices
Example
The religious leader defended the orthodoxy of the faith.
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 /ˌoʊvərˈbɛrɪŋ/

overbearing

Meaning
unpleasantly or arrogantly domineering
Example
His overbearing attitude made everyone uncomfortable.
C2 adjective /ˈɒpjʊlənt/

opulent

Meaning
Ostentatiously rich, luxurious, or lavish.
Example
They hosted an opulent wedding with gold decorations.
B1 adverb /əˈkeɪʒənəli/

Occasionally

Meaning
sometimes; from time to time; not regularly
Example
I occasionally visit my grandmother on weekends.
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.
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 noun/verb /ˌoʊvərˈlæp/

overlap

Meaning
To extend over and cover partly; an area where things coincide.
Example
The two meetings overlap by an hour.
A1 pronoun /aʊər/

our

Meaning
belonging to or associated with the speaker and one or more other people
Example
This is our house.
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 noun /oʊf/

Oaf

Meaning
a clumsy, stupid, or insensitive person
Example
Don't be such an oaf - handle the dishes carefully!
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.
A1 pronoun /ˈʌðərz/

others

Meaning
people or things distinct from the ones already mentioned or known
Example
I like to spend time with others.
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.
B2 verb /əˈrɪdʒɪneɪt/

originate

Meaning
to come into existence; to begin; to create or produce
Example
The tradition originated in ancient times.
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.
B2 noun /əbˈsɛʃən/

obsession

Meaning
An idea, thought, or concern that continually preoccupies or intrudes on a person's mind.
Example
His obsession with success drove him to work day and night.
C1 adjective /ɔːˈneɪt/

ornate

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

overt

Meaning
Done or shown openly; not hidden or secret.
Example
There was an overt display of hostility between the rivals.
C1 noun /ˈɒf.sprɪŋ/

offspring

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

optometry

Meaning
The practice or profession of examining the eyes and prescribing corrective lenses.
Example
She studied optometry at the university to become an eye specialist.
B2 verb /ˌoʊvərˈpeɪ/

overpay

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