Nasty cut in garment (5)
I believe the answer is:
tunic
'garment' is the definition.
(tunic is a kind of garment)
'nasty cut in' is the wordplay.
'nasty' is an anagram indicator.
'cut'+'in'='cutin'
'cutin' anagrammed gives 'TUNIC'.
(Other definitions for tunic that I've seen before include "Dress for soldier" , "Belted coat" , "piece of clothing" , "Upper garment, for a soldier say" , "Policeman may be in one" .)