lunatic(noun, adjective) adjective1. insane and believed to be affected by the phases of the moonSimilar word(s): insane, moonstruck noun1. an insane personSimilar word(s): madman, maniacDefinition categories: person, sufferer2. a reckless impetuous irresponsible personSimilar word(s): daredevil, hothead, madcap, swashbucklerDefinition categories: person, adventurer, venturer