key (on a piano, organ, etc.)

keyboard (of a piano, typewriter, etc.)

keyhole

keyhole

bunch of keys

locksmith

private account (on social media, esp. Twitter), account that can only be viewed by approved followers

private account (on social media, esp. Twitter), account that can only be viewed by approved followers

key rack, (wall-mounted) key holder, key hook

key ring

key-shaped

key-shaped

key bed

black key (on a piano, organ, etc.)

keystroke

duplicate key, master key, passkey...

latchkey child, latchkey kid

locking doors, lock and key, vital point

hidden mysteries, secret principle

to become locked, to lock

internal lock

white key (on a piano, organ, etc.)

section of road that is curved on purpose as a defensive measure

telegraph key (switching device used to send Morse code)

lock-opening, lock-picking

key rack, (wall-mounted) key holder, key hook

square bracket, Japanese-style quotation marks

key management

duplicate key, master key, passkey...

to become locked, to lock