Englishfor English speakers
assistant
Noun
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An assistant is a person who helps (or assists) another person.
The doctor's assistant held his tools.
assistant
Adjective
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If you are assistant, you have a position under someone.
The assistant guard was in training to become a full guard.
contribution
Noun
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A contribution is something that you give or add.
Technology to reduce pollution could make a significant contribution to the solution.
Some of his most important early contributions were his detailed descriptions and illustrations.
Their contribution in October has been revised down from £300million to the same level.
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The money you give to someone, especially for a donation, is your contribution.
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The amount of work you did on a project.
His contribution was very low. He did almost nothing.
officer
Noun
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An officer is a person in an army who has much authority. A general and a captain are two types of officers.
A soldier must obey his commanding officer.
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An officer is a policeman, often called a "police officer." (Note, "officer" is often better than "policeman" because the officer could be a woman or a man.)
Officer, can you help me, I've been robbed.
The thief was taken to jail by the officers.
He was arrested for hitting an officer.
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An officer is someone who holds office (meaning, has authority).
The judge is an important officer of the court.
She is the chief executive officer, or CEO, for our company.