Crazy outfit with 'gangster' song (8)
I believe the answer is:
madrigal
'song' is the definition.
(madrigal is a kind of song)
'crazy outfit with gangster' is the wordplay.
'crazy' becomes 'mad' ('mad' can be a synonym of 'crazy').
'outfit' becomes 'rig' ('rig' can be a synonym of 'outfit'**).
'with' is a charade indicator (letters next to each other).
'gangster' becomes 'al' (Al Capone).
'mad'+'rig'+'al'='MADRIGAL'
(Other definitions for madrigal that I've seen before include "Unaccompanied song in several parts" , "Unaccompanied harmonised part song" , "glee" , "Part song for unaccompanied voices" , "Elizabethan song" .)