Ship concealing most of gun, I hear (8)
I believe the answer is:
listener
'i hear' is the definition.
(someone who hears things)
'ship concealing most of gun' is the wordplay.
'ship' becomes 'liner' (liner is a kind of ship).
'concealing' is an insertion indicator.
'most of' means to remove the last letter.
'gun' becomes 'sten' (British sub-machine gun).
'sten' with its final letter taken away is 'ste'.
'liner' enclosing 'ste' is 'LISTENER'.
(Other definitions for listener that I've seen before include "One hearing" , "One giving attention" , "Radio fan" , "One lending an ear" , "Auditor" .)