Fierce girl enthralling any number (7)
I believe the answer is:
violent
'fierce' is the definition.
('violent' can be a synonym of 'fierce')
'girl enthralling any number' is the wordplay.
'girl' becomes 'violet'.
'enthralling' indicates putting letters inside.
'any number' becomes 'n' (I've seen this in other clues).
'violet' going around 'n' is 'VIOLENT'.
(Other definitions for violent that I've seen before include "Sharp" , "Extreme(ly aggressive)" , "Brutal - intense" , "Furious" , "Using extreme physical force" .)