Antonyms are words that have an opposite meaning to the word being described. In the case of "cyclic insanity," the opposite could be "mental stability," "balance of mind," or "sanity." Unlike cyclic insanity, which is a recurrent mental disorder characterized by extreme mood swings, irritability, and irrational behavior, mental stability refers to a natural state of emotional and psychological balance. A sane person is rational, clear-eyed, and able to perceive reality. In contrast, "cyclic insanity" is a severe mental disorder where people experience intense episodes of mania or depression. Therefore, antonyms for this term would include stable, logical, rational, and responsible.