Source : Webster's Revised Unabridged Dictionary (1913)

Decrepit \De*crep"it\, a. [L. decrepitus, perhaps orig., noised
   out, noiseless, applied to old people, who creep about
   quietly; de- + crepare to make a noise, rattle: cf. F.
   d['e]cr['e]pit. See {Crepitate}.]
   Broken down with age; wasted and enfeebled by the infirmities
   of old age; feeble; worn out. ``Beggary or decrepit age.''
   --Milton.

         Already decrepit with premature old age. --Motley.

   Note: Sometimes incorrectly written decrepid.

Source : WordNet®

decrepit
     adj 1: worn and broken down by hard use; "a creaky shack"; "a
            decrepit bus...its seats held together with friction
            tape"; "a flea-bitten sofa"; "a run-down
            neighborhood"; "a woebegone old shack" [syn: {creaky},
             {flea-bitten}, {run-down}, {woebegone}]
     2: lacking physical strength or vitality; "a feeble old woman";
        "her body looked sapless" [syn: {debile}, {feeble}, {infirm},
         {sapless}, {weak}, {weakly}]