The Collaborative International Dictionary of English v.0.48:

Titty \Tit"ty\, n.
   A little teat; a nipple. [Familiar]
   [1913 Webster]

WordNet (r) 3.0 (2006):

titty
    n 1: either of two soft fleshy milk-secreting glandular organs
         on the chest of a woman [syn: breast, bosom, knocker,
         boob, tit, titty]