Want to carry gun but denied (7)
I believe the answer is:
negated
'denied' is the definition.
(I've seen this before)
'want to carry gun' is the wordplay.
'want' becomes 'need' (synonyms).
'to carry' is an insertion indicator.
'gun' becomes 'gat' (US informal term for a gun).
'need' placed around 'gat' is 'NEGATED'.
'but' is the link.
(Other definitions for negated that I've seen before include "Discredited" , "Made ineffective" , "Abrogated" , "Nullified" , "Denied" .)