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late 14c., "moral weakness," from Old French fragilité "debility, frailty" (12c.), from Latin fragilitatem (nominative fragilitas) "brittleness," from fragilis "brittle, easily broken," from root of frangere "to break" (see fraction). Meaning "quality of being easily broken" first recorded in English late 15c.
1510s, "liable to sin, morally weak;" c.1600, "liable to break;" a back-formation from fragility, or else from Middle French fragile (14c.), from Latin fragilis (see fragility). Transferred sense of "frail" (of persons) is from 1858.
fragility fra·gil·i·ty (frə-jĭl'ĭ-tē)
The quality or state of being easily broken or destroyed.