The Collaborative International Dictionary of English v.0.48:

Sapless \Sap"less\, a.
   1. Destitute of sap; not juicy.
      [1913 Webster]

   2. Fig.: Dry; old; husky; withered; spiritless. "A somewhat
      sapless womanhood." --Lowell.
      [1913 Webster]

            Now sapless on the verge of death he stands.
                                                  --Dryden.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sapless
    adj 1: lacking bodily or muscular strength or vitality; "a
           feeble old woman"; "her body looked sapless" [syn:
           decrepit, debile, feeble, infirm, rickety,
           sapless, weak, weakly]
    2: destitute of sap and other vital juices; dry; "the rats and
       roaches scurrying along the sapless planks"- Norman Mailer

Moby Thesaurus II by Grady Ward, 1.0:

94 Moby Thesaurus words for "sapless":
   Saharan, anemic, anhydrous, arid, asthenic, athirst, bland,
   bloodless, bone-dry, chicken, cowardly, dead, debilitated, desert,
   dilute, diluted, driveling, drooping, droopy, droughty, dry,
   dry as dust, dull, dusty, effete, etiolated, fade, faint, faintish,
   feeble, flabby, flaccid, flat, flavorless, floppy, gone, gruelly,
   gutless, high and dry, imbecile, impotent, inane, indifferent,
   innocuous, insipid, jejune, juiceless, languid, languorous,
   like parchment, limber, limp, listless, lustless, marrowless, mild,
   milk-and-water, namby-pamby, nerveless, pappy, pithless, pooped,
   powerless, pulpy, rubbery, sandy, savorless, sinewless, slack,
   soft, spiceless, spineless, stale, strengthless, tasteless, thin,
   thirsting, thirsty, undamped, unflavored, unhardened, unnerved,
   unsavory, unstrung, unwatered, vapid, washy, watered, watered-down,
   waterless, watery, weak, weakly, wishy-washy