Monster keeps clear, seeing this girl (8)
I believe the answer is:
brunette
'this girl' is the definition.
(woman with brunette hair)
'monster keeps clear' is the wordplay.
'monster' becomes 'brute' (I've seen this in another clue).
'keeps' is an insertion indicator.
'clear' becomes 'net' (as in net profit).
'brute' going around 'net' is 'BRUNETTE'.
'seeing' acts as a link.
(Other definitions for brunette that I've seen before include "She's certainly not blond" , "She's certainly not a blonde" , "Unfair woman" , "Dark-haired woman" , "Brown-haired" .)