Dark-haired beast going around trap (8)
I believe the answer is:
brunette
'dark-haired' is the definition.
('brunette' can be similar in meaning to 'dark-haired')
'beast going around trap' is the wordplay.
'beast' becomes 'brute' ('brute' can be a synonym of 'beast'**).
'going around' indicates putting letters inside.
'trap' becomes 'net' (net is a kind of trap).
'brute' going around 'net' is 'BRUNETTE'.
(Other definitions for brunette that I've seen before include "Person with dark brown hair" , "She's certainly not a blonde" , "woman with brown hair" , "Hair colour" , "Woman with dark hair" .)