One way to hold infirm: something that is supposed to hold steady does not hold. Picture a person who reaches for the wall on the way to the kitchen. The legs are still there, but they cannot be counted on any more. Move that picture off the body and you get the rest of the word. A will that keeps shifting, ground that may give way under an argument, a claim whose support has just been .
From the word’s history
The packet's source traces the adjective through Middle English infirme to Latin infirmus, glossed there as weak or feeble, and the verb to Latin infirmare from the same infirmus. So the body sense and the verb are one root, not two.
來源把形容詞一路追到中古英文 infirme，再到拉丁文 infirmus，並把 infirmus 解作「虛弱的、無力的」；動詞則來自同一個 infirmus 變出來的 īnfirmāre。所以身體那一支和動詞那一支同根，不是兩條線。
Wiktionary entries supplied in this packet (kaikki:3f6f69a190036ae4:1109801079:9979 and :1109811058:4917): 'from Latin infirmus (weak, feeble)'; 'The verb is from Latin īnfirmāre, from īnfirmus'
登入就可以看每一支怎麼連回核心畫面。