Cow's chew (3)
I believe the answer is:
cud
'cow's chew' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for cud that I've seen before include "Wad of something chewable" , "Bovines chew it" , "It's chewed by a ruminant" , "Ruminant animals chew it" , "Ruminants chew it (3)" .)