foible (n.)

1640s, "weak point of a sword blade" (contrasted to forte), from French foible "a weak point, a weakness, failing," from noun use of Old French adjective feble "feeble" (see feeble). The spelling borrowed in English is obsolete in modern French, which uses faible. Extended sense of "weak point of character" is first recorded 1670s. Related: Foibles.