The Collaborative International Dictionary of English v.0.48:

gutless \gut"less\ adj.
   lacking courage or vitality; as, he was a yellow gutless
   worm. Opposite of gutsy.

   Syn: spineless.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

gutless
    adj 1: lacking courage or vitality; "he was a yellow gutless
           worm"; "a spineless craven fellow" [ant: gutsy,
           plucky]
    2: weak in willpower, courage or vitality [syn: namby-pamby,
       gutless, spineless, wishy-washy]

Moby Thesaurus II by Grady Ward, 1.0:

63 Moby Thesaurus words for "gutless":
   anemic, asthenic, bloodless, chicken, coward, cowardly, craven,
   debilitated, drooping, droopy, dull, effete, etiolated, faint,
   faintish, feeble, flabby, flaccid, floppy, gone, gritless,
   heartless, imbecile, impotent, languid, languorous, lily-livered,
   limber, limp, listless, lustless, marrowless, nerveless, pithless,
   pluckless, poltroonish, pooped, powerless, pusillanimous, rubbery,
   sapless, sinewless, slack, soft, spineless, spiritless, spunkless,
   strengthless, uncourageous, undaring, ungallant, unhardened,
   unheroic, unintrepid, unmanly, unnerved, unsoldierlike,
   unsoldierly, unstrung, unvaliant, unvalorous, weak, weakly