Mount for a revolver (4)
I believe the answer is:
colt
I believe this is a double definition.
'mount' is the first definition.
(thesaurus)
'a revolver' is the second definition.
(I've seen this before)
'for' is the link.
(Other definitions for colt that I've seen before include "Early American revolver" , "pistol" , "runner" , "Young player" , "Young animal" .)