The Collaborative International Dictionary of English v.0.48:

flabby \flab"by\ (fl[a^]b"b[y^]), a. [See Flap.]
   Yielding to the touch, and easily moved or shaken; hanging
   loose by its own weight; wanting firmness; flaccid; as,
   flabby flesh.
   [1913 Webster]

WordNet (r) 3.0 (2006):

flabby
    adj 1: 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:

78 Moby Thesaurus words for "flabby":
   anemic, asthenic, baccate, baggy, bloodless, chicken, cowardly,
   debilitated, doughy, drooping, droopy, dull, effete, enervated,
   etiolated, faint, faintish, feeble, flaccid, fleshy, flimsy,
   floppy, forceless, gone, gutless, imbecile, impotent, ineffective,
   ineffectual, languid, languorous, lax, limber, limp, listless,
   loose, lustless, macerated, marrowless, masticated, mushy,
   nerveless, pasty, pendulous, pithless, pithy, pooped, powerless,
   pulpal, pulpar, pulped, pulplike, pulpy, quaggy, relaxed, rubbery,
   sagging, sapless, sinewless, slack, sleazy, soft, spineless,
   spiritless, spongy, squashy, squelchy, squishy, strengthless,
   succulent, unhardened, unnerved, unstrung, weak, weakly, yielding,