Oasis
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C1 noun /oʊˈeɪ.sɪs/

Oasis

Meaning
a fertile spot in a desert where water is found; a pleasant refuge
Example
The travelers found an oasis after days in the desert.
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 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 /ˌɒbsəˈliːt/

obsolete

Meaning
No longer in use or out of date.
Example
Floppy disks are now completely obsolete.
B2 adjective ˌɒp.ərˈeɪ.ʃən.əl

operational

Meaning
In working order; ready for use.
Example
The space project will be operational by 2025.
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.
C1 adjective /əbˈnɒkʃəs/

Obnoxious

Meaning
extremely unpleasant; offensive; annoying
Example
His obnoxious behavior at the party annoyed everyone.
C2 noun /ˌɑːbdʒərˈɡeɪʃən/

objurgation

Meaning
a harsh scolding or strong rebuke
Example
His misconduct earned him a severe objurgation from the manager.
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 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 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 /əbˈzɜːrvətɔːri/

observatory

Meaning
A building equipped for observing astronomical or meteorological events.
Example
The observatory is open to the public on weekends.
B2 verb /əˈpoʊz/

oppose

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

Outwardly

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

Occasionally

Meaning
sometimes; from time to time; not regularly
Example
I occasionally visit my grandmother on weekends.
C1 adjective /əbˈstrʌk.tɪv/

Obstructive

Meaning
deliberately creating difficulties or preventing progress; hindering or blocking something
Example
The obstructive policies hindered economic growth.
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.
B1 adjective /ˌoʊld ˈfæʃənd/

old-fashioned

Meaning
not modern; belonging to an earlier time
Example
He still wears an old-fashioned hat.
B2 adjective /aʊtˈreɪdʒəs/

outrageous

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

ostentatious

Meaning
Characterized by a showy or pretentious display intended to impress others.
Example
He wore an ostentatious gold chain to the party.
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.
A1 preposition, adverb /ˈoʊvər/

over

Meaning
across, on top of, or beyond
Example
The book is lying over the table.
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.
B2 noun /ˈaʊtˌbreɪk/

outbreak

Meaning
a sudden start or occurrence of something unpleasant, like disease or violence
Example
There was an outbreak of flu in the city.
C2 verb /ˈɑːskjʊleɪt/

osculate

Meaning
To kiss.
Example
They osculated under the mistletoe during the party.
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 /ˈaʊtˌsɛt/

outset

Meaning
the beginning or start of something
Example
From the outset, the project seemed ambitious but achievable.
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 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.
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.
C1 adjective /ˌɑːpərˈtuːn/

opportune

Meaning
Happening at a suitable or convenient time.
Example
She arrived at an opportune moment to help.
C1 verb /ˌaʊtˈweɪ/

outweigh

Meaning
To be more important, valuable, or significant than something else.
Example
The benefits of the new policy outweigh the risks.
C2 noun /ɔːˈreɪʃən/

oration

Meaning
A formal speech, especially one given on a ceremonial occasion
Example
The president delivered an inspiring oration.
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.
C1 adjective/adverb /ˌɒfˈhænd/

offhand

Meaning
Without previous thought or preparation; casual and sometimes dismissive.
Example
She gave an offhand reply to his serious question.
C1 adjective /ˌaʊtˈlændɪʃ/

outlandish

Meaning
Looking or sounding bizarre or unfamiliar; strange.
Example
He wore an outlandish costume to the festival.
B1 noun ˈɒk.sɪ.dʒən

oxygen

Meaning
A colorless, odorless reactive gas, the chemical element of atomic number 8 and the life-supporting component of the air.
Example
Oxygen is vital for life.
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 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.
C2 adjective /ˈoʊ.pən ˈhɑrt.ɪd/

Open-hearted

Meaning
Kind and generous; sincere and honest; warmly receptive;
Example
She welcomed the strangers with an open-hearted smile and invited them for dinner.
C2 adjective /ˈɒkjʊlər/

ocular

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

Oath

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

objector

Meaning
a person who expresses opposition or disapproval to something
Example
The objector raised his concerns during the town meeting.
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 /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.
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 /ɒmˈnɪpətəns/

omnipotence

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

outride

Meaning
to ride faster, farther, or better than someone else
Example
The young rider managed to outride his competitors in the race.
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 /ˈɒksɪdənt/

occident

Meaning
The countries of the West, especially Europe and America.
Example
The Occident has a long history of philosophical thought.
B2 noun /ˈaʊt.saɪ.dər/

Out-sider

Meaning
a person who does not belong to a particular group; someone not accepted by a group
Example
As an outsider, he found it difficult to understand their traditions.
C1 verb /ˌaʊtˈduː/

outdo

Meaning
To do better than someone else; to surpass.
Example
She always tries to outdo her classmates in exams.
B2 verb /əˈblaɪdʒ/

oblige

Meaning
to compel or require someone to do something; to help or do a favor
Example
I would be happy to oblige you with the information you need.
C2 adjective /ˈɒfɪʃ/

offish

Meaning
Unfriendly, distant, or reserved in manner.
Example
He seemed offish at the party and avoided most conversations.
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 /ˈɑn.set/

Onset

Meaning
the beginning or early stages of something; the start of a medical condition
Example
The onset of winter brought heavy snowfall.
C2 adjective /ˈəʊ.dər.əs/

Odorous

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

onslaught

Meaning
A fierce or destructive attack.
Example
The village faced an onslaught of enemy forces.
C2 adjective /ˈoʊ.kən/

oaken

Meaning
made of or resembling oak wood
Example
The villagers gathered around the oaken table in the hall.
B2 noun /ˈɔːkɪstrə/

orchestra

Meaning
a large group of musicians playing different instruments together
Example
The orchestra performed beautifully at the concert.
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.
B2 verb /ˌoʊvərˈsiː/

oversee

Meaning
to supervise or watch over something; to manage and direct
Example
The manager will oversee the entire construction project.
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 /əbˈzɜːrvənt/

Observant

Meaning
quick to notice things; watchful; attentive
Example
The observant detective noticed every small detail at the crime scene.
C2 verb /ˈɔːreɪt/

orate

Meaning
To speak in a formal, often pompous manner
Example
He began to orate at the ceremony.
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.
C1 adjective /ˈɒptɪməm/

optimum

Meaning
Most conducive to a favorable outcome; best.
Example
To achieve optimum results, we need to improve efficiency.
C2 adjective /ɑːlˈfæktəri/

olfactory

Meaning
Relating to the sense of smell.
Example
The perfume activated her olfactory nerves immediately.
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.
C1 adjective /ˌɔːrnəˈmɛntl/

ornamental

Meaning
Serving as decoration; decorative rather than functional.
Example
The garden was filled with ornamental plants.
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 adjective /ˈɒptɪkəl/

optical

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

Optional

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

obeisance

Meaning
A gesture of respect such as a bow or curtsy.
Example
They bowed in obeisance to the king.
C2 noun ˈɒpjʊləns

opulence

Meaning
Great wealth or luxuriousness.
Example
The opulence of the mansion was evident in its ornate furnishings.
C1 noun /ˈaʊtˌkraɪ/

outcry

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

offense

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

obsequious

Meaning
Excessively obedient or attentive in a servile way.
Example
The waiter gave an obsequious bow to every customer.
C1 adjective /ˌaʊt əv ðə ˈweɪ/

out-of-the-way

Meaning
remote or unusual; not in a convenient or usual location
Example
They stayed in an out-of-the-way village.
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.
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 /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 /ˈoʊ.ʃən/

ocean

Meaning
A very large expanse of sea, especially the main areas of sea between continents.
Example
The ocean covers more than 70% of the Earth's surface.
C1 noun /ˈɒf.sprɪŋ/

offspring

Meaning
a person's child or children; an animal's young
Example
The bird carefully fed its offspring.
B2 adjective /ˌɑːp.təˈmɪs.tɪk/

optimistic

Meaning
hopeful and confident about the future
Example
She is optimistic about the success of her new project.
B2 verb /ˌoʊvərˈiːt/

overeat

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

outreach

Meaning
The act of providing services or support to people who might not otherwise have access to them.
Example
The charity launched a new outreach program for the homeless.
C1 adjective /ˈaʊt.kɑːst/

Outcast

Meaning
rejected by society; excluded person
Example
He felt like an outcast in his new school.
B1 adverb /əˈrɪdʒɪnəli/

originally

Meaning
in the beginning, at first
Example
Originally, she wanted to be a doctor.
C1 adjective ˈɒb.stɪ.nət

obstinate

Meaning
Refusing to change one's mind or accept others' advice easily.
Example
He remained obstinate despite the logical arguments.
A1 adverb /ɔːf/

off

Meaning
away from a place, position, or time; not functioning
Example
He turned off the light before leaving the room.
B2 verb /ˌoʊvərˈtɜrn/

overturn

Meaning
to turn something upside down or to reverse a decision or judgment
Example
The court decided to overturn the previous ruling.
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 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.
C1 adjective /ˌoʊvərˈbloʊn/

overblown

Meaning
excessively exaggerated or inflated
Example
The controversy was overblown by the media.
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.
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 adjective /əˈprəʊ.bri.əs/

opprobrious

Meaning
Expressing strong criticism or scorn.
Example
He made opprobrious remarks about his opponent.
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 /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.
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.
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.
C2 verb ˈɑːb.fə.skeɪt

obfuscate

Meaning
Render obscure, unclear, or unintelligible.
Example
Politicians often obfuscate facts to mislead people.
B2 noun /əbˈzɜːvər/

observer

Meaning
a person who watches or notices something
Example
The observer took notes 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.
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.
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 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.