Is he short of a goat? (5)
I believe the answer is:
billy
This clue is a double definition.
'is he short' is the first definition.
(short for William; 'short' suggests an abbreviation)
'a goat?' is the second definition.
(billy is a kind of goat)
'of' acts as a link.
(Other definitions for billy that I've seen before include "... boy" , "Goat; camper's kettle" , "Camp can" , "Camper's pot" , "Cooking can for William" .)