The Collaborative International Dictionary of English v.0.48:

Tit \Tit\, n.
   1. A small horse. --Tusser.
      [1913 Webster]

   2. A woman; -- used in contempt. --Burton.
      [1913 Webster]

   3. A morsel; a bit. --Halliwell.
      [1913 Webster]

   4. [OE.; cf. Icel. titter a tit or small bird. The word
      probably meant originally, something small, and is perhaps
      the same as teat. Cf. Titmouse, Tittle.] (Zool.)
      (a) Any one of numerous species of small singing birds
          belonging to the families Paridae and
          Leiotrichidae; a titmouse.
      (b) The European meadow pipit; a titlark.
          [1913 Webster]

   Ground tit. (Zool.) See Wren tit, under Wren.

   Hill tit (Zool.), any one of numerous species of Asiatic
      singing birds belonging to Siva, Milna, and allied
      genera.

   Tit babbler (Zool.), any one of several species of small
      East Indian and Asiatic timaline birds of the genus
      Trichastoma.

   Tit for tat. [Probably for tip for tap. See Tip a slight
      blow.] An equivalent; retaliation.

   Tit thrush (Zool.), any one of numerous species of Asiatic
      and East Indian birds belonging to Suthora and allied
      genera. In some respects they are intermediate between the
      thrushes and titmice.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Titmouse \Tit"mouse`\, n.; pl. Titmice. [OE. titemose,
   titmase; tit small, or a small bird + AS. m[=a]se a kind of
   small bird; akin to D. mees a titmouse, G. meise, OHG. meisa,
   Icel. meisingr. The English form has been influenced by the
   unrelated word mouse. Cf. Tit a small bird.] (Zool.)
   Any one of numerous species of small insectivorous singing
   birds belonging to Parus and allied genera; -- called also
   tit, and tomtit.
   [1913 Webster]

   Note: The blue titmouse (Parus coeruleus), the marsh
         titmouse (Parus palustris), the crested titmouse
         (Parus cristatus), the great titmouse (Parus
         major), and the long tailed titmouse (Aegithalos
         caudatus), are the best-known European species. See
         Chickadee.
         [1913 Webster]

WordNet (r) 3.0 (2006):

tit
    n 1: either of two soft fleshy milk-secreting glandular organs
         on the chest of a woman [syn: breast, bosom, knocker,
         boob, tit, titty]
    2: the small projection of a mammary gland [syn: nipple,
       mammilla, mamilla, pap, teat, tit]
    3: small insectivorous birds [syn: titmouse, tit]

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "tit":
   bag, bantam, banty, boobs, bosom, breast, breasts, brisket, bust,
   button, chest, chit, crop, diminutive, dug, featherweight,
   fingerling, knockers, lightweight, mama, mamelon, mamelonation,
   mammary gland, mammilla, mammillation, mini, minikin, minnow,
   minny, mouse, nenes, nipple, nubbin, pap, papilla, peewee,
   pigeon breast, pony, runt, shrimp, slip, small fry, snip, snippet,
   teat, thorax, tits, titties, titty, udder, wart, wisp