The Collaborative International Dictionary of English v.0.48:

Helpless \Help"less\, a.
   1. Destitute of help or strength; unable to help or defend
      one's self; needing help; feeble; weak; as, a helpless
      infant.
      [1913 Webster]

            How shall I then your helpless fame defend? --Pope.
      [1913 Webster]

   2. Beyond help; irremediable.
      [1913 Webster]

            Some helpless disagreement or dislike, either of
            mind or body.                         --Milton.
      [1913 Webster]

   3. Bringing no help; unaiding. [Obs.]
      [1913 Webster]

            Yet since the gods have been
            Helpless foreseers of my plagues.     --Chapman.
      [1913 Webster]

   4. Unsupplied; destitute; -- with of. [R.]
      [1913 Webster]

            Helpless of all that human wants require. --Dryden.
      -- Help"less*ly, adv. -- Help"less*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

helpless
    adj 1: lacking in or deprived of strength or power; "lying ill
           and helpless"; "helpless with laughter" [syn: helpless,
           incapacitated]
    2: unable to function; without help [syn: helpless, lost]
    3: unable to manage independently; "as helpless as a baby"

Moby Thesaurus II by Grady Ward, 1.0:

85 Moby Thesaurus words for "helpless":
   abandoned, aidless, at sea, baffled, bare-handed, bewildered,
   blind, blind drunk, blotto, confounded, confused, crippled,
   debilitated, defenseless, dependent, deserted, desolate, disabled,
   enervated, enfeebled, exhausted, faint, fatherless, feeble,
   forlorn, forsaken, friendless, godforsaken, guardless, guideless,
   helpless, homeless, impotent, incapable, incompetent, inefficient,
   inept, infirm, kithless, lame, leaderless, motherless, muddled,
   mystified, nonplussed, out, out cold, outcast, overcome, paralyzed,
   passed out, perplexed, pregnable, prostrate, spent, stiff, stoned,
   unarmed, unarmored, unattended, unavailing, uncovered, undefended,
   under the table, unfit, unfortified, unfriended, ungarrisoned,
   unguarded, unprotected, unqualified, unscreened, unsheltered,
   unshielded, unsuspecting, untenable, unwarned, unwatched, useless,
   vulnerable, weak, weakened, weaponless, worn out, worthless