What a belt encircles (5)
I believe the answer is:
waist
'what a belt encircles' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for waist that I've seen before include "Narrow part of body" , "Middle of trunk" , "Central part of body" , "Band may go round here" , "Middle part of a ship" .)