1. secret, esoteric, occult, cryptic. Mysterious, inscrutable, mystical, obscure refer to that which is not easily comprehended or explained. That which is mysterious by being unknown or puzzling, excites curiosity, amazement, or awe: a mysterious disease. Inscrutable applies to that which is impenetrable, so enigmatic that one cannot interpret its significance: an inscrutable smile. That which is mystical has a secret significance, such as that attaching to certain rites or signs: mystical symbols. That which is obscure is discovered or comprehended dimly or with difficulty: obscure motives. 3. unfathomable, unintelligible, incomprehensible, enigmatic, impenetrable.