Cow's milk gland (5)
I believe the answer is:
udder
'cow's milk gland' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for udder that I've seen before include "Milk producing gland of cows etc" , "Natural container for milk?" , "Animal mammary gland" , "Animal organ with more than one teat" , "Cow's milk "bag"" .)