Garment tenor's wearing split from behind (5)
I believe the answer is:
pants
'garment' is the definition.
(pants is a kind of garment)
'tenor's wearing split from behind' is the wordplay.
'tenor' becomes 't'.
'wearing' is an insertion indicator.
'split' becomes 'snap' (both can mean to break).
'from behind' is a reversal indicator.
't' placed inside 'snap' is 'stnap'.
'stnap' back-to-front is 'PANTS'.
(Other definitions for pants that I've seen before include "Briefs" , "boxers?" , "Shocking" , "Rubbish (slang) - undergarment" , "Shorts" .)