In disguise, slip round to get the gun (6)
I believe the answer is:
pistol
'the gun' is the definition.
(pistol is a kind of gun)
'in disguise slip round to' is the wordplay.
'in disguise' indicates an anagram.
'round' means one lot of letters goes inside another.
'slip' is an anagram of 'pisl'.
'pisl' going around 'to' is 'PISTOL'.
'get' is the link.
(Other definitions for pistol that I've seen before include "Small gun" , "Piece" , "Type of gun" , "Arm" , "Officer's side-arm" .)