From The Collaborative International Dictionary of English v.0.48 [gcide]:
Usage: An infirmity belongs, for the most part, to particular members, and is often temporary, as of the eyes, etc. Debility is more general, and while it lasts impairs the ordinary functions of nature. Imbecility attaches to the whole frame, and renders it more or less powerless. Debility may be constitutional or may be the result or superinduced causes; Imbecility is always constitutional; infirmity is accidental, and results from sickness or a decay of the frame. These words, in their figurative uses, have the same distinctions; we speak of infirmity of will, debility of body, and an Imbecility which affects the whole man; but Imbecility is often used with specific reference to feebleness of mind.
From WordNet (r) 3.0 (2006) [wn]:
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