obscure
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B2 adjective, verb /əbˈskjʊr/

obscure

Meaning
Not clearly expressed or understood; to make something difficult to see or understand.
Example
The meaning of the poem was obscure to most readers.
B2 noun /ˌɑb.zɚˈveɪ.ʃən/

Observation

Meaning
the action of watching something carefully; a comment or remark
Example
The scientist made careful observations of the experiment.
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.
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.
A2 adjective /ˈɔː.dɪ.nər.i/

Ordinary

Meaning
normal; usual; not special
Example
It was just an ordinary day at the office.
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.
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.
A2 adjective /ɒd/

Odd

Meaning
strange; unusual; different from what is normal or expected
Example
That's an odd way to solve the problem.
B1 noun /ˌɒpəˈreɪʃən/

operation

Meaning
an act or process of functioning or operating
Example
The hospital performed a successful operation.
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 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The process of becoming obsolete or outdated and no longer used.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 /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 /ˌɔːrəˈtɔːri.oʊ/

oratorio

Meaning
A large-scale musical composition for orchestra, choir, and soloists, usually on a sacred theme, performed without costumes or scenery.
Example
Handel's 'Messiah' is one of the most famous oratorios ever written.
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.
C1 adjective /ˌoʊvərˈbɛrɪŋ/

overbearing

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

odious

Meaning
extremely unpleasant or repulsive
Example
The dictator was remembered for his odious crimes.
C1 noun /əbˈdʒɛktər/

objector

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

opposed

Meaning
being against or in disagreement with something
Example
She is strongly opposed to animal testing.
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.
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 noun /ˈaʊtˌkraɪ/

outcry

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

Obloquy

Meaning
harsh criticism or verbal abuse; strong public condemnation
Example
The politician faced obloquy after the scandal.
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.
A1 adjective /əʊˈkeɪ/

okay

Meaning
used to express agreement or acceptance
Example
It's okay to leave early today.
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.
C1 adjective /əˈblɪɡ.ə.tɔː.ri/

obligatory

Meaning
Required by a legal, moral, or other rule; compulsory.
Example
Wearing a seatbelt is obligatory in most countries.
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.
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.
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.
B1 adjective /əˈrɪdʒ.ɪ.nəl/

Original

Meaning
first; fundamental; primary; authentic
Example
This is the original document, not a copy.
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 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.
B2 noun /əbˈdʒek.ʃən/

Objection

Meaning
an expression of disagreement or disapproval; a reason for disagreeing
Example
The lawyer raised an objection during the trial.
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.
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 əʊˈpeɪk

opaque

Meaning
Not able to be seen through; not transparent; difficult to understand.
Example
The glass was too opaque to see through.
C1 noun /ˈaʊtpoʊst/

outpost

Meaning
A small military camp or position at some distance from the main force, used especially as a guard.
Example
The soldiers were stationed at a remote outpost.
A2 adverb; noun /ˌaʊtˈdɔːrz/

outdoors

Meaning
outside a building; the natural environment outside
Example
We spent the whole afternoon outdoors enjoying the fresh air.
B2 noun /ˈaʊtbɜːrst/

outburst

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

ostracism

Meaning
The act of excluding someone from a group or society.
Example
The student faced ostracism after breaking the rules.
C2 adjective /ˌɒbsəˈlɛsnt/

obsolescent

Meaning
Becoming outdated or on the way to becoming obsolete.
Example
The obsolescent technology could not compete with modern devices.
B2 verb /ˌoʊvərˈloʊd/

overload

Meaning
to load with too much weight or cargo; to give too much work or information
Example
Don't overload the washing machine or it might break down.
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 /ˈɒktəɡən/

octagon

Meaning
A polygon with eight sides and eight angles.
Example
The stop sign is shaped like an octagon.
C2 adjective /əbˈstrɛpərəs/

obstreperous

Meaning
Noisy and difficult to control.
Example
The obstreperous students disrupted the class.
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.
C2 noun /ˈɒlɪv bɑːb/

Olive barb

Meaning
A small freshwater fish with olive-colored body and barbels
Example
The olive barb is commonly found in South Asian rivers.
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 noun /ˌɔːrnɪˈθɒlədʒɪst/

ornithologist

Meaning
a scientist who studies birds
Example
The ornithologist spent years studying migratory birds.
C2 adjective /əˈprəʊ.bri.əs/

opprobrious

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

overcome

Meaning
To succeed in dealing with a problem or difficulty.
Example
You can overcome procrastination with planning.
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 oʊˈbiː.sə.t̬i

obesity

Meaning
The condition of being grossly fat or overweight.
Example
Obesity increases the risk of diabetes and heart disease.
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.
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.
C1 noun /ˈɒf.sprɪŋ/

offspring

Meaning
a person's child or children; an animal's young
Example
The bird carefully fed its offspring.
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.
C2 adjective /ˈɒf.biːt/

offbeat

Meaning
Unusual, unconventional, or different from the norm.
Example
She has a very offbeat sense of humor.
C2 noun /ˈɒksɪdənt/

occident

Meaning
The countries of the West, especially Europe and America.
Example
The Occident has a long history of philosophical thought.
C1 noun /ˈɒfʃuːt/

offshoot

Meaning
A branch or result that develops from something larger or more important.
Example
The startup was an offshoot of a major tech 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.
C1 adjective /əbˈzɜːrvənt/

Observant

Meaning
quick to notice things; watchful; attentive
Example
The observant detective noticed every small detail at the crime scene.
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.
A1 verb, adjective /oʊn/

own

Meaning
to possess something; belonging to oneself
Example
She owns a beautiful house in the city.
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 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.
B2 adjective /ˌoʊvərˈwɛlmɪŋ/

overwhelming

Meaning
Very intense; overpowering.
Example
Large tasks can feel overwhelming.
B2 adjective /aʊtˈreɪdʒəs/

outrageous

Meaning
Shockingly bad or excessive; very unusual or amusing.
Example
The comedian told an outrageous joke.
C1 noun /ˈɒptɪks/

optics

Meaning
The branch of physics dealing with light and vision.
Example
She studied optics to understand how lenses work.
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.
B2 noun /ɔːˈræŋ.ʊˌtæŋ/

Orang-Outang

Meaning
a large arboreal ape with long reddish hair, long arms, and hooked hands and feet, native to Borneo and Sumatra
Example
The orangutan swings gracefully through the forest canopy.
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.
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.
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 /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 /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 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 verb /ˈɒfsɛt/

offset

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

objurgate

Meaning
to scold or rebuke severely
Example
The teacher objurgated the student for being dishonest.
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 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.
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 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 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.
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.
A2 preposition /ˈɒntu/

onto

Meaning
moving to a position on the surface of something
Example
She jumped onto the table to get the book.
B2 noun /ˈaʊtˌfɪt/

outfit

Meaning
A set of clothes worn together, often for a particular occasion.
Example
She wore a beautiful outfit to the party.
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.
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 verb /uːz/

ooze

Meaning
to slowly flow or leak out through small openings or pores
Example
Blood began to ooze from the small cut.
C1 adjective /əbˈtjuːs/

Obtuse

Meaning
annoyingly insensitive or slow to understand; lacking in intelligence or perception
Example
He was being deliberately obtuse about the instructions.
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 /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.
B1 noun ˌɔː.ɡən.aɪˈzeɪ.ʃənz

organizations

Meaning
Organized groups of people with a particular purpose
Example
Organizations play a key role in policymaking.
C2 verb ˈɑːb.fə.skeɪt

obfuscate

Meaning
Render obscure, unclear, or unintelligible.
Example
Politicians often obfuscate facts to mislead people.
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.
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.
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.
C2 adjective /ˌoʊpəˈlɛsənt/

opalescent

Meaning
showing or reflecting a milky, iridescent light like an opal
Example
The opalescent sky glowed with shades of pink and blue.
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 /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.
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.
A2 modal verb /ɔːt/

ought

Meaning
Used to indicate duty, correctness, or moral obligation.
Example
You ought to respect your elders.
C1 noun /ˈɑːdəsi/

odyssey

Meaning
a long, adventurous journey; a series of experiences
Example
Her career has been an odyssey of challenges and achievements.
A1 adverb /ˈɔːfən/

often

Meaning
frequently, many times
Example
I often visit my grandparents on weekends.
B2 adjective /ˈɔɪl.i/

Oily

Meaning
covered with oil; containing oil; greasy
Example
Her oily skin needs special care.
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.
A1 adjective /ˈʌðər/

other

Meaning
used to refer to something different from the one already mentioned or known
Example
I don't want this one, I will take the other one.
C2 adjective /ɑːlˈfæktəri/

olfactory

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

Oath

Meaning
a solemn promise or declaration; a sworn statement
Example
The doctor took an oath to help patients.
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.
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.
C2 adjective /ˈɒfɪʃ/

offish

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