Very masculine domain (5)
I believe the answer is:
realm
'domain' is the definition.
(I've seen this before)
'very masculine' is the wordplay.
'very' becomes 'real' ('real' can be similar in meaning to 'very').
'masculine' becomes 'm'.
'real'+'m'='REALM'
(Other definitions for realm that I've seen before include "Empire - state" , "Province" , "World" , "Knowledge base" , "department" .)