Aggressively masculine (5)
I believe the answer is:
macho
'aggressively masculine' is the definition.
(macho means aggressively masculine)
This is the entire clue.
(Other definitions for macho that I've seen before include "Aggressively male" , "Jock" , "Exaggeratedly masculine" , "Affectedly virile" , "Ultra-masculine" .)