vertical

standing or pointing straight up or at an angle of 90° to a horizontal surface or line

• She looked over the cliff and found she was standing at the edge of a vertical drop.

obscure

not known to many people

• an obscure island in the Pacific

extent

area or length; amount

• We don't yet know the extent of his injuries (= how bad his injuries are).

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the degree to which something happens or is likely to happen

• She had not realized the extent to which the children had been affected.

extend

to add to something in order to make it bigger or longer

• We have plans to extend our house (= to make it bigger).

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to stretch something out

• He extended his hand as a greeting (= held out his hand for someone to shake it).

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to offer or give something to someone

• I should like to extend my thanks to you for your kindness.

optics

the study of light and of instruments using light

excess

an amount that is more than acceptable, expected, or reasonable

• An excess of enthusiasm is not always a good thing.

expel

to force someone to leave a school, organization, or country

• he new government has expelled all foreign diplomats.

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to force air or liquid out of something

• When you breathe out, you expel air from your lungs.

expenditure

the total amount of money that a government or person spends

• he new* government has expelled all foreign diplomats.

the act of using or spending energy, time, or money

• The expenditure of effort on this project has been enormous.

expansion

the increase of something in size, number, or importance

• the rapid expansion of the software industry

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commercial

related to buying and selling things

• The commercial future of the company looks very promising.

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glimpse

to see something or someone for a very short time or only partly

• We glimpsed the ruined abbey from the windows of the train.

gasoline

• formal for gas

balcony

an area with a wall or bars around it that is joined to the outside wall of a building on an upper level

• We had a drink on the hotel balcony.

optimistic

hoping or believing that good things will happen in the future

• She is optimistic about her chances of winning a gold medal.

optional

If something is optional, you can choose if you want to do it, pay it, buy it, etc.

• English is compulsory for all students, but art and music are optional.

offend

to make someone upset or angry

• I think she was offended that she hadn't been invited to the party.

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to commit a crime

• Obviously if a police officer offends it's a fairly serious matter.

internal

existing or happening inside a person, object, organization, place, or country

• The bank conducted its own internal investigation into the robbery.

racial

happening between people of different races

• He had a vision of a society living in racial harmony.

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connected with someone's race

• They are members of a racial minority.

radiation

a form of energy that comes from a nuclear reaction and that can be very dangerous to health

• Many servicemen suffered radiation sickness after the early atomic tests. hollow

recommend

to suggest that someone or something would be good or suitable for a particular job or purpose, or to suggest that a particular action should be done

• She has been recommended for promotion.

adhere

to stick firmly

• A smooth, dry surface helps the [tiles]瓷磚) adhere to the wall.

capture

to take someone as a prisoner, or to take something into your possession, especially by force

• Two of the soldiers were killed and the rest were captured.

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to succeed in getting something when you are competing with other people

• The Democratic Party captured 70 percent of the vote.

valid

based on truth or reason; able to be accepted

• My way of thinking might be different from yours, but it's equally valid.

---

A ticket or other document is valid if it is based on or used according to a set of official conditions that often include a time limit

• My passport is valid for another two years.

continual

happening repeatedly, usually in an annoying or not convenient way

• I've had continual problems with this car ever since I bought it.

continuous

• My computer makes a continuous low buzzing noise.

exploit

to use something in a way that helps you

• We need to make sure that we exploit our resources as fully as possible.

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to use someone or something unfairly for your own advantage

• Laws exist to stop companies exploiting their employees.

remote

far away in distance or time, or not closely related

• It happened in the remote past, so no one worries about it any more.

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A remote area, house, or village is a long way from any towns or cities.

• a remote mountain village

removal

the act of taking something or someone away from somewhere or something

• furniture removal

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the act of forcing someone to leave an important position or job

• There have been calls for the president's removal.

precaution

an action that is done to prevent something unpleasant or dangerous happening

• Many people have been stockpiling food as a precaution against shortages.

• If you're going to have sex, make sure you take precautions.

idle

not working or being used

• Half these factories now stand idle.

poverty

the condition of being extremely poor

• Two million people in the city live in abject (= very great) poverty.

resistant

not wanting to accept something, especially changes or new ideas

• Why are you so resistant to change?

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not harmed or affected by something

• a disease-resistant variety of tomato