Cream derived from goat grease (9)
I believe the answer is:
butterfat
'cream' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'goat grease' is the wordplay.
'goat' becomes 'butter' (something which 'butts').
'grease' becomes 'fat'.
'butter'+'fat'='BUTTERFAT'
'derived from' is the link.
Can you help me to learn more?
(Other definitions for butterfat that I've seen before include "Ingredient of milk" , "Dairy product" .)