Cartilage (7)
I believe the answer is:
gristle
'cartilage' is the definition.
(synonyms)
This is all the clue.
(Other definitions for gristle that I've seen before include "Stir leg to get tough tissue in meat" , "Glister with animal tissue" , "Stir leg (anag.)" , "Inedible cartilage" , "Sinew" .)