Mammal that chews the cud (8)
I believe the answer is:
ruminant
'mammal that chews the cud' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for ruminant that I've seen before include "Cud-chewing animal" , "contemplative" , "Mammal that chews the cud" , "Animal that chews the cud" , "Beast that chews the cud" .)