Meaning of “key” - Learner’s Dictionary

key

noun [ C ] uk us /kiː/
FOR LOCKS

A1 a piece of metal cut into a particular shape and used for locking things such as doors, or for starting an engine:

I've lost my car keys.
METHOD

B1 a way of explaining or achieving something:

Hard work is the key to success.
KEYBOARD

B2 one of the parts you press with your fingers on a keyboard or musical instrument to produce letters, numbers, or to make a sound

MUSIC

a set of musical notes based on one particular note:

the key of D major
SYMBOLS

a list that explains the symbols on a map or picture

ANSWERS

A2 a list of answers to an exercise or game

→ See also under lock and key

(Definition of “key noun” from the Cambridge Learner’s Dictionary © Cambridge University Press)