Teat

Teats are what mammals use to feed their babies. They let milk be taken by the young. Milk is digested by the babies with a special hormone. 
The number and position of the teats varies with the species. Humans are different to most mammals in that they may continue to drink milk throughout life. Normal mammals stop digesting milk at a certain stage. This forces the young to change to an adult diet.
The word "teat" is from the Old French or Dutch word, "tete" or the Greek word "τιτθύς".