The Collaborative International Dictionary of English v.0.48:

Feeble \Fee"ble\ (f[=e]"b'l), a. [Compar. Feebler (-bl[~e]r);
   superl. Feeblest (-bl[e^]st).] [OE. feble, OF. feble,
   flebe, floibe, floible, foible, F. faible, L. flebilis to be
   wept over, lamentable, wretched, fr. flere to weep. Cf.
   Foible.]
   1. Deficient in physical strength; weak; infirm; debilitated.
      [1913 Webster]

            Carried all the feeble of them upon asses. --2
                                                  Chron. xxviii.
                                                  15.
      [1913 Webster]

   2. Wanting force, vigor, or efficiency in action or
      expression; not full, loud, bright, strong, rapid, etc.;
      faint; as, a feeble color; feeble motion. "A lady's feeble
      voice." --Shak.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Feeble \Fee"ble\, v. t.
   To make feble; to enfeeble. [Obs.]
   [1913 Webster]

         Shall that victorious hand be feebled here? --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

feeble
    adj 1: pathetically lacking in force or effectiveness; "a feeble
           excuse"; "a lame argument" [syn: feeble, lame]
    2: lacking strength or vigor; "damning with faint praise";
       "faint resistance"; "feeble efforts"; "a feeble voice" [syn:
       faint, feeble]
    3: lacking bodily or muscular strength or vitality; "a feeble
       old woman"; "her body looked sapless" [syn: decrepit,
       debile, feeble, infirm, rickety, sapless, weak,
       weakly]
    4: lacking strength; "a weak, nerveless fool, devoid of energy
       and promptitude"- Nathaniel Hawthorne [syn: feeble,
       nerveless]

Moby Thesaurus II by Grady Ward, 1.0:

201 Moby Thesaurus words for "feeble":
   abulic, afraid, aged, ailing, anemic, anile, asthenic, backward,
   barely audible, blear, bleared, bleary, bloodless, blurred, blurry,
   cachectic, chicken, confused, cowardly, crabbed, dark, debilitated,
   decrepit, decrescendo, delicate, dim, dim-witted, distant, dizzy,
   doddered, doddering, doddery, drained, drooping, droopy, dull,
   effete, emasculated, enervated, enfeebled, etiolated, exhausted,
   failing, faint, faint-voiced, fainthearted, faintish, feckless,
   feebleminded, filmy, flabby, flaccid, flimsy, floppy, foggy,
   forceless, fossilized, fragile, frail, fuzzy, gentle, gerontal,
   gerontic, gone, gutless, half-baked, half-heard, half-seen,
   half-visible, half-witted, hazy, healthless, helpless, ill-defined,
   imbecile, imperceptible, impotent, impuissant, in poor health,
   inadequate, inconclusive, inconspicuous, indefinite, indistinct,
   indistinguishable, ineffective, ineffectual, infirm, insignificant,
   insubstantial, insufficient, invalid, invertebrate, lame, languid,
   languishing, languorous, limber, limp, listless, low, low-profile,
   lustless, marrowless, merely glimpsed, misty, moribund, moronic,
   mossbacked, moth-eaten, mummylike, murmured, namby-pamby,
   nerveless, obscure, out of focus, pale, palsied, paltry,
   papery-skinned, peaked, peaky, pianissimo, piano, pithless,
   pliable, pooped, poor, powerless, puny, ravaged with age, reduced,
   reduced in health, rickety, rubbery, run to seed, run-down, rusty,
   sapless, scarcely heard, semivisible, senile, shadowy, shaky,
   shoddy, shriveled, sickly, simpleminded, sinewless, slack, slight,
   slow, slow-witted, soft, soft-sounding, soft-voiced, spineless,
   spiritless, strengthless, stricken in years, subaudible, subdued,
   thin, timeworn, tottering, tottery, unavailing, uncertain, unclear,
   unconvincing, undefined, unhardened, unhealthy, unmanned, unnerved,
   unplain, unproved, unrecognizable, unrigorous, unsatisfactory,
   unsound, unstrung, unsubstantial, unsustained, vague,
   valetudinarian, valetudinary, weak, weak-kneed, weak-minded,
   weak-voiced, weak-willed, weakened, weakly, wet, whispered,
   wishy-washy, with low resistance, withered, wizened, woozy