Very fierce about women using bad language (8)
I believe the answer is:
swearing
'using bad language' is the definition.
(I've seen this before)
'very fierce about women' is the wordplay.
'very fierce' becomes 'searing' (eg searing heat).
'about' means one lot of letters goes inside another.
'women' becomes 'w' (standard abbreviation).
'searing' enclosing 'w' is 'SWEARING'.
(Other definitions for swearing that I've seen before include "Using bad language" , "Foul language" , "promising" , "Vowing" , "Taking an oath" .)