The Collaborative International Dictionary of English v.0.48:

Debilitate \De*bil"i*tate\, v. t. [imp. & p. p. Debilitated;
   p. pr. & vb. n. Debilitating.] [L. debilitatus, p. p. of
   debilitare to debilitate, fr. debilis. See Debility.]
   To impair the strength of; to weaken; to enfeeble; as, to
   debilitate the body by intemperance.
   [1913 Webster]

         Various ails debilitate the mind.        --Jenyns.
   [1913 Webster]

         The debilitated frame of Mr. Bertram was exhausted by
         this last effort.                        --Sir W.
                                                  Scott.
   [1913 Webster]

WordNet (r) 3.0 (2006):

debilitate
    v 1: make weak; "Life in the camp drained him" [syn: enfeeble,
         debilitate, drain]

Moby Thesaurus II by Grady Ward, 1.0:

94 Moby Thesaurus words for "debilitate":
   abate, afflict, attenuate, beat, blunt, bugger, burn out, cramp,
   cripple, damp, dampen, de-energize, deaden, derange, devitalize,
   disable, disenable, disorder, do in, do up, drain, dull, enervate,
   enfeeble, eviscerate, exhaust, extenuate, fag, fag out, fatigue,
   flag, frazzle, gruel, hamstring, harass, hors de combat,
   hospitalize, hurt, inactivate, incapacitate, indispose, invalid,
   jade, kibosh, knock out, knock up, lame, lay low, lay up, maim,
   mar, mitigate, overfatigue, overstrain, overtire, overweary, poop,
   poop out, prostrate, put, queer, queer the works, rattle, reduce,
   sabotage, sap, shake, shake up, sicken, soften up, spike, spoil,
   tire, tire out, tire to death, tucker, unbrace, undermine, unfit,
   unman, unnerve, unstrengthen, unstring, use up, weaken, wear,
   wear down, wear on, wear out, weary, wilt, wind, wing, wreck