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English words starting with O — with CEFR levels

239 words from A1 to C2. Click a word to learn it in its unit.

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A1o’clockadv · used with a number for the exact hour
A2oakn · a large tree with hard wood
B2oathn · a formal promise, often in public
B2obediencen · doing what you are told
B2obedientadj · doing what you are told
B2obeyv · to follow a rule or order
B2obituaryn · a notice about someone who has died
B1objectn · a thing you can see or touch
B2objectv · to say that you disagree
B1objectionn · a reason for disagreeing with something
B1objectiven · a goal
B2objectiveadj · based on facts, not on personal opinions
B2obligationn · something you must do by duty or law
C1obligev · to make someone feel they must do something
C2obliqueadj · indirect, not stated openly
C1obscurev/adj · to make something hard to see or understand
C1obscurelyadv · in an unclear or hard-to-see way
B1observationn · something seen and noted carefully
B1observev · to watch carefully
B2observern · a person who watches something closely
B2obsessv · to think about something too much
B2obsessionn · a strong, constant interest that fills the mind
B2obsessiveadj · thinking about one thing too much
B1obstaclen · something that stops you from succeeding
B1obtainv · to get
B1obviousadj · easy to see or understand
B1obviouslyadv · in a way that is easy to see
B1occasionn/v · a particular event or time
B1occasionaladj · happening sometimes, not often
B1occasionallyadv · sometimes, not often
C1occupantn · a person who lives in a place
A2occupationn · a job or profession
C1occupationaladj · related to a person’s job
B1occupyv · to live or be in a place
B1occurv · to happen
B1oceann · a very large area of sea
A1Octobern · the tenth month of the year
C2octogenariann · a person aged between eighty and eighty-nine
B2oddadj · strange or unusual
C1oddityn · a strange person or thing
A1ofprep · belonging to; about; made from
A1offadj · not on; not working
A2offadv · not working; away
B1offprep · away from a place or surface
B2offendv · to make someone feel upset or insulted
B2offendern · a person who has broken the law
B2offensen · an illegal act or crime
B1offensiveadj · rude and upsetting
A2offern/v · something you sell cheaply or give
B2offhandadv · without preparation or much thought
A1officen · a room or building for work
A1officern · a person in a police or army job
A2officialadj · made or accepted by a government
B2officialn · a person with a position of authority
B1officiallyadv · in a formal and public way
B2offshoreadj · located abroad or out at sea
C1offspringn · the young animals or children of a parent
A1oftenadv · many times
A2oiln · a liquid used for cooking
B1oilyadj · containing or covered with oil
B2ointmentn · a soft cream for skin
A1OKadj/adv · fine; all right
A1oldadj · having lived for many years
B1old-fashionedadj · not modern
B2oliven · a small green or black fruit with oil
A2olive oiln · oil made from olives
B2Olympian · a famous ancient place in Greece
B2Olympiadn · an international competition, often for students
A2Olympicadj · about the world’s biggest sports event
A1Olympicsn · a big international sports event
A2omeletn · eggs mixed and cooked flat in a pan
A1onprep · touching the top of something
A2onadv · working; in operation
A1onceadv · one time only
B2onceconj · as soon as; when
A1onedet/num · the number 1
A2onepron · a thing already mentioned
B1oneselfpron · a person’s own self (used for people in general)
A2onionn · a round vegetable with a strong smell
A2onlineadj/adv · using the internet
A1onlyadj/adv · one and no more
B1onstageadj · on or at the stage in a theatre
B1ontoprep · to a position on top of something
C2opacityn · the quality of not letting light through
C2opaqueadj · not clear; impossible to see through
A1openv/adj · to move something so it is not closed
B1openingn · the start of a public event or place
B2openlyadv · honestly, without hiding anything
A1operan · a play where people sing
A2operatev · to make a machine work
B1operationn · medical treatment that cuts into the body
B2operatorn · a person who works a machine or switchboard
A2opinionn · what you think about something
B2opponentn · a person you compete against
A2opportunityn · a chance to do something good
A2opposev · to be against something
A2oppositeadj/prep · on the other side facing
B1oppositen/adv · completely different in meaning
B1oppositionn · the political parties not in government
B1oppressv · to treat people in a cruel and unfair way
B1oppressionn · cruel treatment by those in power
B2optimismn · a positive way of looking at things
B2optimistn · a person who expects good outcomes
B2optimisticadj · expecting good things to happen
B1optionn · something you can choose
B2optionaladj · not required; you can choose
C2opulencen · great wealth and luxury
C2opulentadj · looking rich and luxurious
C2opulentlyadv · in a rich, luxurious way
A1orconj · used to show a choice
B1oraln · spoken, not written
B2oraladj · spoken, not written
A1orangen/adj · a round fruit with thick skin
B2oratorn · a skilled public speaker
B1orbitn · the path of an object around a planet
C1orchardn · a field of fruit trees
B1orchestran · a large group of musicians
B2orchestraladj · relating to a large group of musicians
B2orchidn · a delicate flower in many colors
C2ordainv · to order officially by law or authority
A1ordern · a request for food or goods
A2orderv · to ask for food in a restaurant
B1orderlyadj · well arranged and well behaved
C1ordinarilyadv · usually; in normal circumstances
B1ordinaryadj · normal, not special
C2oren · rock containing useful metal
B1organn · a body part with a special job
B1organicadj · grown without chemicals
B1organismn · a living thing, such as a plant or animal
B1organizationn · a group of people with a shared purpose
C1organizationaladj · relating to how a group or event is organized
A2organizev · to plan and arrange something
A2organizedadj · good at planning things well
B2organizern · a person who plans and arranges an event
B1originn · the place or time where something starts
A2originaladj · the first one, not a copy
B2originaln · the first thing from which copies are made
B2originalityn · being new and different
B2originallyadv · at the beginning, in the first place
B2originatev · to begin or come from
B2ornamentn · a small decorative object
C1ornamentaladj · grown or made for decoration
C2ornateadj · decorated with fancy details
A2orphann · a child whose parents have died
C1orphanv · to leave a child without parents
C2ostensibleadj · stated or seeming, but perhaps not real
C2ostensiblyadv · apparently, but not truly
A1otherdet · different; not this one
A2otherpron · the second or remaining people or things
B1otherwiseadv · if not; or else
C1ottern · a small water animal with a long body
B1ought tomodal · should
B2ouncen · a small unit of weight, about 28 grams
A1ourdet · belonging to us
A1ourspron · belonging to us
A2ourselvespron · used when we do something by our own
A1outadv · away from the inside of a place
A2out ofprep · from inside to outside
B1out-of-dateadj · old and no longer modern or useful
B2outbackn · remote dry land far from towns
B2outbreakn · a sudden start of a disease or trouble
B2outcomen · the result of something
B2outdistancev · to go much farther or faster than others
B2outdov · to do better than someone else
B1outdooradj · done outside
B1outdoorsadv · outside, not in a building
B1outeradj · on the outside
B2outfitn · a set of clothes worn together
B2outgrowv · to become too big for something
B2outingn · a short trip for pleasure
B1outlawn · a criminal who is hiding from the law
B2outletn · a shop selling goods directly from a maker
B1outlinev · to describe the main points
B2outlinen · a short plan or main points of something
B2outlivev · to live longer than another person or thing
B2outlookn · what is expected to happen in the future
C2outmodedadj · no longer useful or fashionable
B2outpatientn · a patient who does not stay overnight
B2outputn · the amount of something produced
B2outragen · strong anger about something unfair
B2outrageousadj · shocking and unacceptable
C1outsetn · the beginning of something
B2outshinev · to be much better than others
A1outsideadv · not in a building
A2outsideprep · not inside; near the front of a place
B2outsiden/adj · the outer part or surface of something
B2outsidern · a person who does not belong to a group
B2outskirtsn · the outer parts of a town or city
B1outstandingadj · extremely good
B1outwardadj · seen on the outside
B2outwardlyadv · in the way something appears
B1outweighv · to be greater or more important than something
B2ovaladj · shaped like an egg; a long round shape
A2ovenn · a box in a kitchen for baking food
A1overprep · above something
A2overadv · finished
B2overalladj/adv · taking everything into account
C1overallsn · loose clothes worn to protect other clothes
B2overboardadv · over the side of a ship into water
B2overbookv · to sell more tickets than there are places
B2overcoatn · a long warm coat worn over other clothes
B1overcomev · to defeat a problem
C1overdraftn/v · money taken from a bank beyond your balance
B2overemphasizev · to give too much importance to something
B2overestimatev · to think something is bigger or better than it is
B2overhearv · to hear what others say without them knowing
B1overjoyedadj · extremely happy
B2overlapn · a part that two things share
C2overlayv · to cover a surface with a layer
B2overlookv · to fail to notice something
B2overlyadv · too much; more than necessary
B1overnightadj/adv · during the night
A2overseasadv · in or to another country across the sea
B2overseasadj · in or from another country across the sea
C1overseev · to manage and check that work is done
C1overseern · a person who supervises other workers
B2overshadowv · to make something seem less important
B2oversizeadj · bigger than the usual size
B2overstepv · to go beyond what is allowed
B2overtakev · to pass a vehicle ahead
B2overthrowv · to remove a leader or government by force
B2overtimen/adv · extra time worked beyond normal hours
B2overturnv · to turn upside down
A2overweightadj · too heavy for your body size
B1overwhelmv · to be too much for someone to deal with
B1overwhelmingadj · very strong
B1overworkn · working too much
B2own · a sound people make when something hurts
B1owev · to have to pay money back
B1owingadj · because of (used with "to")
B2owing toprep · because of
B2owln · a night bird with big eyes
A1ownadj · belonging to you alone
A2ownpron · belonging to yourself
B1ownv · to have something as your property
A1ownern · a person who has something
B2oxn · a large strong farm animal like a bull
B1oxygenn · a gas in air we need to breathe
B2ozonen · a gas layer high above the Earth