The Collaborative International Dictionary of English v.0.48:

Tipsy \Tip"sy\, a. [Compar. Tipsier; superl. Tipsiest.]
   [Akin to tipple; cf. Prov. G. tips drunkenness, betipst
   drunk, tipsy. See Tipple.]
   1. Being under the influence of strong drink; rendered weak
      or foolish by liquor, but not absolutely or completely
      drunk; fuddled; intoxicated.
      [1913 Webster]

   2. Staggering, as if from intoxication; reeling.
      [1913 Webster]

            Midnight shout and revelry,
            Tipsy dance and jollity.              --Milton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tipsy
    adj 1: slightly intoxicated [syn: potty, tiddly, tipsy]
    2: unstable and prone to tip as if intoxicated; "a tipsy boat"

Moby Thesaurus II by Grady Ward, 1.0:

77 Moby Thesaurus words for "tipsy":
   addled, aslant, aslope, atilt, beery, bemused, besotted, bevel,
   beveled, bias, biased, blind drunk, boozy, canting, careening,
   crapulent, crapulous, dazed, dizzy, drenched, drunk, drunken,
   far-gone, flustered, fou, full, gay, giddy, glorious, happy,
   in liquor, inclinational, inclinatory, inclined, inclining,
   inebriate, inebriated, inebrious, intoxicated, jolly, leaning,
   listing, maudlin, mellow, merry, muddled, nappy, oiled,
   out of plumb, out of square, pitched, raking, recumbent, reeling,
   shelving, shelvy, shikker, sideling, sidelong, slant, slanted,
   slanting, slantways, slantwise, sloped, sloping, sodden, sotted,
   stewed, tiddly, tight, tilted, tilting, tipped, tipping,
   under the influence, unsteady