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English definition of “key”

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key

noun [C] uk   /kiː/ us  

key noun [C] (LOCK)

A1 a piece of metal that has been cut into a special shape and is used for opening or closing a lock, starting a car engine, etc.: car/door keys
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key noun [C] (PART)

B2 any of the set of moving parts that you press with your fingers on a computer keyboard, or musical instrument to produce letters, numbers, symbols, or musical notes
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key noun [C] (MUSICAL NOTES)

a set of musical notes based on one particular note: The song changes key halfway through. the key of C minor

key noun [C] (SYMBOLS)

a list of the symbols used in a map or book with explanations of what they mean

key noun [C] (ANSWERS)

A2 a list of the answers to the questions in an exercise or test: See the key to test 3 on page 176.

key

adjective uk   /kiː/ us  
B2 very important and having a lot of influence on other people or things: She was a key figure in the international art world. a key factor in tackling the problem
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(Definition of key from the Cambridge Advanced Learners Dictionary & Thesaurus © Cambridge University Press)
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