Cut on head: not upset? Absolutely (7)
I believe the answer is:
tonsure
'cut on head' is the definition.
(bald area created by a monk's haircut)
'not upset? absolutely' is the wordplay.
'upset?' shows that the letters should be reversed in order (I've seen 'upsets' mean this).
'absolutely' becomes 'sure'.
'not' written backwards gives 'ton'.
'ton'+'sure'='TONSURE'
(Other definitions for tonsure that I've seen before include "Result of shaving" , "Shaven area on monk's head" , "Monastic haircut" , "Shaven part of monk's head" , "Monk's haircut" .)