"infirm" in the adjective sense
1. decrepit, debile, feeble, infirm, rickety, sapless, weak, weakly
lacking bodily or muscular strength or vitality
"a feeble old woman"
"her body looked sapless"
lacking firmness of will or character or purpose give me the daggers" - Shakespeare
"infirm of purpose
Source: WordNet® (An amazing lexical database of English)
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