Fire off the gun in the boat (7)
I believe the answer is:
frigate
'boat' is the definition.
(thesaurus)
'fire off the gun in' is the wordplay.
'off' is an anagram indicator.
'the gun' becomes 'gat' (US informal term for a gun).
'in' indicates putting letters inside.
'fire' is an anagram of 'frie'.
'frie' enclosing 'gat' is 'FRIGATE'.
'the' acts as a link.
(Other definitions for frigate that I've seen before include "Warship; -- bird" , "Type of warship" , "Ship" , "Warship - seabird" , "US warship" .)