Sheep fat (6)
(Other definitions for tallow that I've seen before include "Candle or soap substance" , "Animal fat used in making soap" , "Fat used for soap/candles" , "Candle ingredient" , "Candle grease" .)
'sheep fat' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for suet that I've seen before include "Solid fat used in cooking" , "Hard white cooking fat" , "Edible fat used in cooking" , "Fatty stuff used in cooking" , "Hard edible fat" .)