Melt down, as fat (6)
I believe the answer is:
render
'melt down as fat' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for render that I've seen before include "put a coat on before decorating" , "Provide (a service); cover with plaster" , "Melt down like fat" , "Sing a song or melt fat" , "Sacred choral work" .)