IMBECILITY

stupidity, betise, folly, foolishness, imbecility

(noun) a stupid mistake

imbecility

(noun) retardation more severe than a moron but not as severe as an idiot

Source: WordNet® 3.1

Noun

imbecility (countable and uncountable, plural imbecilities)

The quality of being imbecile; weakness; feebleness, especially of mind.

Something imbecilic; a stupid action, behaviour, etc.

Source: Wiktionary

Im`be*cil"i*ty, n.; pl. Imbecilities. Etym: [L. imbecillitas: cf. F. imbécillité.]

Definition: The quality of being imbecile; weakness; feebleness, esp. of mind. Cruelty . . . argues not only a depravedness of nature, but also a meanness of courage and imbecility of mind. Sir W. Temple.

Note: This term is used specifically to denote natural weakness of the mental faculties, affecting one's power to act reasonably or intelligently.

Syn.

– Debility; infirmity; weakness; feebleness; impotence. See Debility.

Source: Webster’s Unabridged Dictionary 1913 Edition