The Collaborative International Dictionary of English v.0.48:

Dissipate \Dis"si*pate\, v. i.
   1. To separate into parts and disappear; to waste away; to
      scatter; to disperse; to vanish; as, a fog or cloud
      gradually dissipates before the rays or heat of the sun;
      the heat of a body dissipates.
      [1913 Webster]

   2. To be extravagant, wasteful, or dissolute in the pursuit
      of pleasure; to engage in dissipation.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

dissipate \dis"si*pate\ (d[i^]s"s[i^]*p[=a]t), v. t. [imp. & p.
   p. Dissipated; p. pr. & vb. n. Dissipating.] [L.
   dissipatus, p. p. of dissipare; dis- + an obsolete verb
   sipare, supare. to throw.]
   1. To scatter completely; to disperse and cause to disappear;
      -- used esp. of the dispersion of things that can never
      again be collected or restored.
      [1913 Webster]

            Dissipated those foggy mists of error. --Selden.
      [1913 Webster]

            I soon dissipated his fears.          --Cook.
      [1913 Webster]

            The extreme tendency of civilization is to dissipate
            all intellectual energy.              --Hazlitt.
      [1913 Webster]

   2. To destroy by wasteful extravagance or lavish use; to
      squander.
      [1913 Webster]

            The vast wealth . . . was in three years dissipated.
                                                  --Bp. Burnet.

   Syn: To disperse; scatter; dispel; spend; squander; waste;
        consume; lavish.
        [1913 Webster]

WordNet (r) 3.0 (2006):

dissipate
    v 1: to cause to separate and go in different directions; "She
         waved her hand and scattered the crowds" [syn: disperse,
         dissipate, dispel, break up, scatter]
    2: move away from each other; "The crowds dispersed"; "The
       children scattered in all directions when the teacher
       approached"; [syn: disperse, dissipate, scatter,
       spread out]
    3: spend frivolously and unwisely; "Fritter away one's
       inheritance" [syn: fritter, frivol away, dissipate,
       shoot, fritter away, fool, fool away]
    4: live a life of pleasure, especially with respect to alcoholic
       consumption

Moby Thesaurus II by Grady Ward, 1.0:

124 Moby Thesaurus words for "dissipate":
   ablate, attenuate, be consumed, be gone, be promiscuous, blow,
   blow off, blunder away, break up, burn up, carouse, cast forth,
   cease, cease to be, cease to exist, chase women, clear away,
   come to naught, come to nothing, commit adultery, consume, crumble,
   debauch, decrease, dematerialize, depart, deplete, depreciate, die,
   die away, die out, diffuse, dilute, diminish, disappear,
   disintegrate, dispel, disperse, disseminate, dissolve, distribute,
   do a fade-out, drain, dribble away, drive away, dwindle, erode,
   evanesce, evaporate, exhaust, exit, fade, fade away, fade out,
   flee, fly, fool, fornicate, fritter away, gamble away, go, go away,
   go through, go to pot, go to seed, go to waste, grovel,
   hang the expense, hide, lavish, leak, leak away, leave no trace,
   leave the scene, live hard, make merry, melt, melt away, party,
   pass, pass away, pass out, perish, peter out, philander,
   plunge into dissipation, rake, retire from sight, revel, roister,
   run riot, run through, run to seed, run to waste, scatter,
   seize the day, shrink, sink, sink away, slather, sleep around, sow,
   sow broadcast, spread out, squander, suffer an eclipse, swing,
   thin, thin out, throw away, throw money around, use up, vanish,
   vanish from sight, vaporize, volatilize, wallow, wanton, waste,
   waste away, wear, wear away, whore, womanize