| oil rig
| noun
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| a structure and machinery used for drilling into the ground in search of oil and gas
| Some oil rigs are used at sea, while others are used on land.
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| oil slick
| noun
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| a patch of oil, usually spilled accidentally, that floats on the surface of the sea
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| oil tanker
| noun
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| a ship that transports huge amounts of oil.
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| ointment
| noun
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| a substance that you put on your skin or on a wound to make it better.
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| old
| adjective
| v1
| having been in use for a long time
| An old teddy bear
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| olive
| noun
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| a small, oval fruit that grows in countries near the Mediterranean Sea.
| Olives are eaten in salads and crushed to make olive oil.
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| Olympic Games
| noun
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| a sporting competition for athletes from countries all over the world that is held every four years.
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| omit
| verb
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| to leave something out, or not to do something.
| His name was omitted from the list.
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| onion
| noun
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| a small, round root vegetable with a strong taste.
| Onions have a thin, papery skin with many layers inside.
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| only
| adjective
| v1
| without any others.
| He’s the only person wearing green.
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| only
| adverb
| v1
| just
| There were only a few beads left in the box.
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| open
| adjective
| v1
| not closed or shut, so that people or things can go in and out.
| Open car doors
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| opera
| noun
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| a musical play where the words are sung instead of spoken.
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| operate
| verb
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| to work a piece of machinery.
| You must be careful when operating machinery
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| opinion
| noun
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| a person’s belief or judgment about something.
| Who is the best football player, in your opinion?
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| opponent
| noun
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| someone who is on the opposite side in a fight or competition.
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| opportunity
| noun
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| a chance, or a suitable time to do something
| He had the opportunity to go to Europe for a year.
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| oppose
| verb
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| to argue or fight against someone or something
| They opposed the decision to close the park
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| opposite
| adjective
| v1
| on the other side.
| He saw his friend on the opposite side of the river.
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| optician
| noun
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| a person whose job is to test peoples’ sight and to sell eyeglasses and contact lenses.
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| optimistic
| adjective
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| expecting or hoping that things will go well.
| Optimistic about the future
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| option
| noun
| v1
| a choice.
| You have several options: you can travel by car, train, or plane
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| orange
| noun
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| a color made by mixing red and yellow together.
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| orangutan
| noun
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| a large ape that lives in tropical forests in Southeast Asia
| Orangutans eat mainly fruit, but also eat leaves, bark, and birds’ eggs. They live in nests called platforms, which they build in trees.
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| orbit
| verb
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| to move around a planet, a moon, or the Sun in space.
| The Earth orbits the Sun.
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| orchard
| noun
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| an area of land where fruit trees are grown.
| They were picking apples in the orchard.
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| orchestra
| noun
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| a large group of musicians who play together
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| orchid
| noun
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| a type of plant with flowers that are an unusual shape.
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| order
| noun
| v1
| an instruction telling someone to do something.
| He gave them orders to stop.
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| ordinary
| adjective
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| not different or unusual in any way.
| His sandwich was fairly ordinary, but she had a special one.
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