mysticism, the practice of religious ecstasies (religious experiences during alternate states of consciousness), together with whatever ideologies, ethics, rites, myths, legends, and magic may be related to them.
The term mystic is derived from the Greek noun mystes, which originally designated an initiate of a secret cult or mystery religion. In Classical Greece (5th–4th century bce) and during the Hellenistic Age (323 bce–330 ce), the rites of the mystery religions were largely or wholly secret. The term mystes is itself derived from the verb myein (“to close,” especially the eyes or mouth) and signified a person who kept a secret. Early Christianity appropriated the technical vocabulary of the Hellenistic mysteries but later disavowed secrecy, resulting in a transformation of the meaning of mystes. In subsequent Christian usage, mystes, or mystic, referred to practitioners of doctrinally acceptable forms of religious ecstasy.