n. Insanity in which there is a more or less complete limitation of the perverted mental action to a particular field, as a specific delusion, or an impulse to do some particular thing. The other mental functions may show some signs of degeneration.n. In popular use, an unreasonable zeal for or interest in some one thing; a craze.n. Synonyms Lunacy, Derangement, etc. See insanity.