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English definition of “key”

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key

noun  /ki/ us  

key noun (METAL SHAPE)

[C] a piece of metal cut into a special shape to fit into a lock where it can be turned to open something, such as a door, or to start something, such as a car engine: I put the key into the ignition.

key noun (MOVABLE PART)

[C] any of the set of movable parts that you press with your fingers on a computer or other machine to produce letters, numbers, or symbols, or on a musical instrument to produce sound: piano keys Press the shift key to write in capital letters.

key noun (IMPORTANT PART)

[U] the most important part of achieving something or explaining a situation: Revision is the key to good writing.

key noun (MUSICAL NOTES)

music [C] a set of musical notes based on one particular note: the key of C

key noun (LIST OF SYMBOLS)

[C] a list of the symbols used in a map or book with explanations of what they mean: The key is printed at the bottom of the page.
key
adjective  /ki/ us  
Deception is a key element of military strategy.
(Definition of key from the Cambridge Academic Content Dictionary © Cambridge University Press)
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