Idiocy

n. [Gr. ἰδιωτεία, from ἰδιώτης. See IDIOT, and cf. IDIOTCY.] The condition of being an idiot, or idiotic; natural absence or marked deficiency of sense and intelligence.

I will undertake to convict a man of idiocy, if he can not see the proof that three angles of a triangle are equal to two right angles. F. W. Robertson.