Unfortunate cut in garment (5)
I believe the answer is:
'garment' is the definition.
(tunic is a kind of garment)
'unfortunate cut in' is the wordplay.
'unfortunate' is an anagram indicator.
'cutin' with letters rearranged gives 'TUNIC'.
(Other definitions for tunic that I've seen before include "School garment", "Cut in (anag)", "Close-fitting jacket that's part of a uniform", "top", "Close fitting jacket as part of uniform".)