a small specially shaped piece of metal that you put into a lock and turn in order to lock or unlock a door, start a car etc ! Do not say 'the key of' something. Say the key to something. ➔ master key
I lost my house keys.
A bunch of keys hung from his belt.
the part of a plan, action etc, that will make it possible for it to succeed
the buttons that you press on a computer keyboard to operate the computer:
Press the ESCAPE key to exit.
hot key/shortcut key (=a special key on a computer that does specific things)
a) [usually plural]
the wooden or metal parts that you press on a piano and some wind instruments in order to play them:
a scale of notes that begins with one particular note, or the quality of sound this scale has:
a tune in the key of A minor
a list of the signs, colours etc used on a map or technical drawing etc that explains what they mean
the printed answers to a test or set of questions in a book
a small flat island, especially one that is part of a group near the coast:
the Florida Keys