Solid fat used in cooking (4)
I believe the answer is:
suet
'solid fat used in cooking' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for suet that I've seen before include "Edible fat used in cooking" , "Hard fat in cattle and sheep" , "Edible animal fat" , "Hard animal fat used in cooking" , "Fatty stuff used in cooking" .)