1. stupidity Idiocy is a state of mental unsoundness amounting almost or quite to total absence of understanding. Imbecility is a condition of mental weakness, which may or may not be as complete as that of Synonyms: idiocy, fatuity, foolishness, incapacity, stupidity, folly, imbecility, senselessness Antonyms: acuteness, brilliancy, common sense, sagacity, soundness, astuteness, capacity, intelligence, sense, wisdom