Source : Webster's Revised Unabridged Dictionary (1913)

Holster \Hol"ster\, n. [D. holster; skin to AS. heolstor den,
   cave, fr. helan to conceal, and to Icel. hulstr case, Goth.
   hulistr covering, veil, huljan to cover. [root]17. See {Hele}
   to cover, {Hell}, and cf. {Housing}, {Houss}.]
   A leather case for a pistol, carried by a horseman at the bow
   of his saddle

Source : WordNet®

holster
     n 1: a sheath (usually leather) for a handgun; attaches to a belt
          or saddle
     2: a belt with loops or slots for carrying small hand tools