The Collaborative International Dictionary of English v.0.48:

Teat \Teat\ (t[=e]t), n. [OE. tete, titte, AS. tit, titt; akin
   to LG. & OD. titte, D. tet, G. zitze: cf. F. tette, probably
   of Teutonic origin.]
   1. The protuberance through which milk is drawn from the
      udder or breast of a mammal; a nipple; a pap; a mammilla;
      a dug; a tit.
      [1913 Webster]

   2. (Mach.) A small protuberance or nozzle resembling the teat
      of an animal.
      [1913 Webster]

WordNet (r) 3.0 (2006):

teat
    n 1: the small projection of a mammary gland [syn: nipple,
         mammilla, mamilla, pap, teat, tit]

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "teat":
   bag, boobs, bosom, breast, breasts, brisket, bust, chest, crop,
   dug, knockers, mama, mamelon, mamelonation, mammary gland,
   mammilla, mammillation, nenes, nipple, pap, papilla, pigeon breast,
   thorax, tit, tits, titties, titty, udder