means Mechanical devices that fasten doors, gates, or containers and open only with the right key, combination, or code.

from From Old English 'loc,' meaning a fastening or barrier, with cousins across the Germanic family — Old Norse 'lok' (a lid or covering) and German 'Loch.' The same root branched into the 'lock' of a canal (a barrier holding water) and gave us 'lock' as in a tuft of hair, where the original sense was something twisted or interlinked. The fastening-device meaning is the oldest and most literal: a thing that holds shut.