holster
Concise Oxford English Dictionary © 2008 Oxford University Press:
holster /ˈhəʊlstə, ˈhɒl-/
▶noun a holder for carrying a handgun, typically worn on a belt or under the arm. ▶verb put (a gun) into its holster.
– origin C17: rel. to Du. holster, of unknown origin.
'holster' also found in these Oxford entries:

