Origin and history of feebleness

late 12c., "lacking strength or vigor" (physical, moral, or intellectual), from Old French feble "weak, feeble" (12c., Modern French faible), a dissimilation of Latin flebilis "lamentable," literally "that is to be wept over," from flere "weep, cry, shed tears, lament" (from PIE *bhle- "to howl;" see bleat (v.)). The first -l- was lost in Old French. The noun meaning "feeble person" is recorded from mid-14c.

word-forming element denoting action, quality, or state, attached to an adjective or past participle to form an abstract noun, from Old English -nes(s), from Proto-Germanic *in-assu- (cognates: Old Saxon -nissi, Middle Dutch -nisse, Dutch -nis, Old High German -nissa, German -nis, Gothic -inassus), from *-in-, originally belonging to the noun stem, + *-assu-, abstract noun suffix, probably from the same root as Latin -tudo (see -tude).