Gangster with a gun making you scared (7)
I believe the answer is:
alarmed
'scared' is the definition.
(alarming is a kind of scaring)
'gangster with a gun' is the wordplay.
'gangster' becomes 'al' (Al Capone).
'with a gun' becomes 'armed' (armed with a gun).
'al'+'armed'='ALARMED'
'making you' is the link.
(Other definitions for alarmed that I've seen before include "Frightened, startled" , "In a panic" , "Frightened, scared" , "Fear-stricken" , "as a door handle may be?" .)