locklocklockslockedlocking1verb (locks, locking, locked)to close something with a key: Don't forget to lock the door when you leave.oppositeunlocklock something awayto put something in a place that you close with a key: The paintings are locked away at night.lock somebody into lock a door so that somebody cannot get out: The prisoners are locked in.lock somebody outto lock a door so that somebody cannot get inlock upto lock all the doors and windows of a building: Make sure you lock up before you leave.locklocklocks2nouna metal thing that keeps a door, gate or box closed so that you need a key to open it again: I heard the key turn in the lock.