imbecility (n.) Look up imbecility at
early 15c., "physical weakness, feebleness (of a body part), impotence," from Middle French imbécillité and directly from Latin imbecillitatem (nominative imbecillitas) "weakness, feebleness," from imbecillus "weak, feeble," traditionally said to mean "unsupported" (quasi sine baculo), from assimilated form of in- "not, opposite of" (see in- (1)) + baculum "a stick" (see bacillus). "Weakness in mind" (as opposed to body) was a secondary sense in Latin but was not attested in English until 1620s.