Adjectives

(s)decrepit, debile, feeble, infirm, rickety, sapless, weak, weaklylacking bodily or muscular strength or vitality“a feeble old woman”, “her body looked sapless”

Adverbs

(r)weaklyin a weak or feeble manner or to a minor degree“weakly agreed to a compromise”, “wheezed weakly”, “he was weakly attracted to her”