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]

The Collaborative International Dictionary of English v.0.48:

debilitated \debilitated\ adj.
   1. lacking strength or vigor; weakened.

   Syn: adynamic, asthenic, enervated.
        [WordNet 1.5]

   2. weakened due to illness.

   Syn: enfeebled, infirm, seedy.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

debilitated
    adj 1: lacking strength or vigor [syn: adynamic, asthenic,
           debilitated, enervated]

Moby Thesaurus II by Grady Ward, 1.0:

170 Moby Thesaurus words for "debilitated":
   anemic, anile, apathetic, asthenic, benumbed, blase, bloodless,
   bored, cachectic, castrated, chicken, cowardly, crabbed, dead,
   decrepit, demasculinized, devitalized, doddered, doddering,
   doddery, dopey, dormant, drained, drooping, droopy, drugged, dull,
   effeminized, effete, emasculate, emasculated, enervated, enfeebled,
   etiolated, eunuchized, exanimate, exhausted, fagged, failing,
   faint, fainting, faintish, fatigued, feeble, feeling faint, flabby,
   flaccid, flagging, floppy, footsore, fossilized, frail, frazzled,
   gelded, gerontal, gerontic, gone, good and tired, gutless,
   healthless, heavy, hebetudinous, imbecile, impotent,
   in poor health, inanimate, inert, infirm, invalid, jaded,
   lackadaisical, languid, languishing, languorous, leaden, lethargic,
   lifeless, limber, limp, listless, lumpish, lustless, marrowless,
   moribund, mossbacked, moth-eaten, mummylike, nerveless, numb, pale,
   palsied, papery-skinned, peaked, peaky, phlegmatic, pithless,
   pooped, powerless, ravaged with age, ready to drop, reduced,
   reduced in health, rickety, rubbery, run ragged, run to seed,
   run-down, rusty, sagging, sapless, sated, seedy, senile, shaky,
   shriveled, sickly, sinewless, slack, sleepy, slow, sluggish, soft,
   somnolent, spineless, stagnant, stagnating, strengthless,
   stricken in years, stultified, supine, timeworn, tired,
   tired-winged, toilworn, torpid, tottering, tottery, unhardened,
   unhealthy, unmanned, unnerved, unrefreshed, unrestored, unsexed,
   unsound, unstrung, valetudinarian, valetudinary, vegetable,
   vegetative, wan, way-weary, wayworn, weak, weakened, weakly,
   wearied, weariful, weary, weary-footed, weary-laden, weary-winged,
   weary-worn, wilting, with low resistance, withered, wizened,
   world-weary, worn, worn-down