Webster's Revised Unabridged Dictionary · 1913

Decrepit

Decrepit , adjective

[Latin decrepitus, perhaps orig., noised out, noiseless, applied to old people, who creep about quietly; de- + crepare to make a noise, rattle: compare French décrépit. 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

Sometimes incorrectly written decrepid.