Monk's haircut (7)
I believe the answer is:
tonsure
'monk's haircut' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for tonsure that I've seen before include "Shearing ?" , "Monk's hair style" , "Monk's hairstyle" , "Uncovered area on top" , "Shaven part of monk's head" .)