Cow part (5)
I believe the answer is:
udder
'cow part' is the definition.
('udder' is part of 'cow')
This is the entire clue.
(Other definitions for udder that I've seen before include "Animal mammary gland" , "Milk supply" , "Teat of a cow" , "Animal organ with more than one teat" , "Cow's teat" .)