udder

n. bag-like mammary gland which hangs down and has more than one teat (in a cow, sheep, etc.)

An udder is the mammary organ of female  cattle and some other mammals, including goats and sheep.A cow has one udder and four teats or nipples, while goats have two teats on their udders. A cow's udder can hold up to around 40 litres (10.6 gallons) of milk, and has a total weight of around 50 kg (110 lb).Udder care and hygiene in cows is important in milking, aiding uninterrupted and untainted milk production, and preventing mastitis.
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Udder mammary gland of farm animals. The cow has four quarters and four teats. The rest of the ruminants and the mare have two. [more]Udder - Community and Resources

Noun
1. mammary gland of bovids (cows and sheep and goats)
(synonym) bag
(hypernym) mammary gland, mamma
(part-holonym) cow, moo-cow

(n.)
The glandular organ in which milk is secreted and stored; -- popularly called the bag in cows and other quadrupeds. See Mamma.
  

(n.)
One of the breasts of a woman.