An Etymological Dictionary of Astronomy and Astrophysics

1. A device fitted to a gate, door, drawer, lid, etc, to keep it firmly closed and often to prevent access by unauthorized persons.
   

2. To fasten (a door, gate, etc) or (of a door, etc) to become fastened with a lock, bolt, etc, so as to prevent entry or exit (Dictionary.com).

Etymology (EN): M.E., from O.E. loc “fastening, bar;” cognate with M.L.G. lok, O.H.G. loh “dungeon,” Ger. Loch “opening, hole,” O.N. lok “a cover, lid;” akin to O.E. lucan “to shut.”

Etymology (PE): Qofl, loan from Ar.