鍵を掛ける[kagiwokakeru] to lock
鍵穴[kagiana] keyhole
鍵盤[kenban] keyboard (e.g. piano, computer)
黒鍵[kokken] black keys
打鍵[daken] keystroke

合鍵[aikagi] duplicate key
鍵っ子[kagikko] latchkey child
鍵束[kagitaba] bunch of keys
関鍵[kanken] locking doors