Be inclined to be skinny (4)
I believe the answer is:
lean
I believe this clue is a triple definition!
'be inclined' is the first definition.
('lean' can be a synonym of 'be inclined')
'to be' is the second definition.
(leaning is a kind of being)
'skinny' is the third definition.
(I've seen this before)
(Other definitions for lean that I've seen before include "Thin; rest (against)" , "Incline, bend" , "without success" , "Meagre" , "David ..., director of Ryan's Daughter" .)