imbecility (n.)

early 15c., "physical weakness, feebleness (of a body part), impotence," from Middle French imbécillité and directly from Latin imbecillitatem (nominative imbecillitas) "weakness, feebleness, helplessness," from imbecillus "weak, feeble," of uncertain origin (see imbecile). "Weakness in mind" (as opposed to body) was a secondary sense in Latin but was not attested in English until 1620s.