The Collaborative International Dictionary of English v.0.48:

nerveless \nerve"less\ (n[~e]rv"l[e^]s), a.
   1. Destitute of nerves.
      [1913 Webster]

   2. Destitute of strength or of courage; wanting vigor; weak;
      powerless.
      [1913 Webster]

            A kingless people for a nerveless state. --Byron.
      [1913 Webster]

            Awaking, all nerveless, from an ugly dream.
                                                  --Hawthorne.
      [1913 Webster]

WordNet (r) 3.0 (2006):

nerveless
    adj 1: marked by calm self-control (especially in trying
           circumstances); unemotional; "play it cool"; "keep cool";
           "stayed coolheaded in the crisis"; "the most nerveless
           winner in the history of the tournament" [syn: cool,
           coolheaded, nerveless]
    2: lacking strength; "a weak, nerveless fool, devoid of energy
       and promptitude"- Nathaniel Hawthorne [syn: feeble,
       nerveless]

Moby Thesaurus II by Grady Ward, 1.0:

77 Moby Thesaurus words for "nerveless":
   anemic, asthenic, bloodless, calm, castrated, chicken, coolheaded,
   cowardly, debilitated, demasculinized, devitalized, drooping,
   droopy, dull, effeminized, effete, emasculate, emasculated,
   enervated, etiolated, eunuchized, faint, faintish, feeble, flabby,
   flaccid, floppy, gelded, gone, gutless, imbecile, impotent,
   inexcitable, languid, languorous, limber, limp, listless, lustless,
   marrowless, pithless, pooped, powerless, relaxed, rock-steady,
   rubbery, sapless, sinewless, slack, soft, spineless, steady,
   steady-handed, steady-nerved, steel-nerved, strengthless,
   strong-nerved, unblenching, unblinking, unfaltering, unflinching,
   unhardened, unmanned, unnerved, unnervous, unquivering, unsexed,
   unshaken, unshaky, unshrinking, unstrained, unstrung, untremulous,
   unwavering, weak, weakly, without a tremor