Ruminant (4)
I believe the answer is:
deer
'ruminant' is the definition.
(I know that deer is a type of ruminant)
This is the entire clue.
(Other definitions for deer that I've seen before include "See 23" , "Ruminant(s) -- breed of 13 down" , "maybe does" , "Perhaps fallow" , "Grazing animal(s)" .)