Characteristic behaviour is masculine (9)
I believe the answer is:
mannerism
'characteristic' is the definition.
(thesaurus)
'behaviour is masculine' is the wordplay.
'behaviour' becomes 'manner' (manner is a kind of behaviour**).
'masculine' becomes 'm'.
'manner'+'is'+'m'='MANNERISM'
(Other definitions for mannerism that I've seen before include "Habitual gesture" , "Habitual way of behaving" , "Distinctive personal way of doing something" , "peculiarity" , "Italian art?" .)