Colt, for one (6)
I believe the answer is:
pistol
'colt for one' is the definition.
(I know that Colt is a type of revolver)
This is the entire clue.
(Other definitions for pistol that I've seen before include "A small hand-gun" , "making an appearance in Shakespeare's King Henry V" , "Rectangular" , "Piece" , "Arm" .)