Nipple

In its most general form, a nipple is a structure from which a fluid emanates. More specifically, it is the projection on the breasts or udder of a mammal by which breast milk is delivered to a mother's young. In this sense, it is often called a teat, especially when referring to non-humans. The rubber mouthpiece of a baby bottle or pacifier may also be referred to as a "nipple" or a "teat".

http://en.wikipedia.org/wiki/Nipple