Fat goat? (6)
I believe the answer is:
butter
This clue is a double definition.
'fat' is the first definition.
(I've seen this before)
'goat?' is the second definition.
(something which 'butts')
(Other definitions for butter that I've seen before include "Type of toffee" , "Dairy product" , "Edible fat" , "Fat - type of fly" , "Spread derived from cream" .)