nipple

Concise Oxford English Dictionary © 2008 Oxford University Press:
nipple/ˈnɪpl/

▶noun

• 1 the small projection in which the mammary ducts of female mammals terminate and from which milk can be secreted.

  ■ the corresponding vestigial structure in a male.

  ■ N. Amer. the teat of a feeding bottle.

• 2 a small projection on a machine, especially one from which oil or other fluid is dispensed.

  ■ a short section of pipe with a screw thread at each end for coupling.

– derivatives
nippled adjective.

– origin C16 (also as neble, nible): perh. a dimin. of neb.