Fat-free? (4)
I believe the answer is:
slim
'fat-free?' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for slim that I've seen before include "Shed excess weight" , "Slenderly built" , "Very small; WW2 Burma commander" , "Take off weight as by dieting" , "Annual horse race" .)