The Collaborative International Dictionary of English v.0.48:

flaccid \flac"cid\ (fl[a^]k"s[i^]d or fl[a^]s"s[i^]d), a. [L.
   flaccidus, fr. flaccus flabby: cf. OF. flaccide.]
   Yielding to pressure for want of firmness and stiffness; soft
   and weak; limber; lax; drooping; flabby; as, a flaccid
   muscle; flaccid flesh.
   [1913 Webster]

         Religious profession . . . has become flacced. --I.
                                                  Taylor.
   -- flac"cid*ly (fl[a^]k"s[i^]d*l[y^] or
   fl[a^]s"s[i^]d*l[y^]), adv. -- flac"cid*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

flaccid
    adj 1: drooping without elasticity; wanting in stiffness; "a
           flaccid penis"
    2: out of condition; not strong or robust; incapable of exertion
       or endurance; "he was too soft for the army"; "flabby around
       the middle"; "flaccid cheeks" [syn: soft, flabby,
       flaccid]

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "flaccid":
   anemic, asthenic, bloodless, chicken, cowardly, debilitated,
   drooping, droopy, dull, effete, emasculated, etiolated, faint,
   faintish, feeble, flabby, flimsy, floppy, gone, gutless, imbecile,
   impotent, languid, languorous, lax, limber, limp, listless, loose,
   lustless, marrowless, nerveless, pithless, pooped, powerless,
   relaxed, rubbery, sapless, sapped, sinewless, slack, sleazy, soft,
   spineless, strengthless, unhardened, unnerved, unstrung, weak,
   weakened, weakly