1852, "one who believes in the ability of the living to communicate with the dead via a medium," from spiritual + -ist (also see spirit (n.)). Earlier (1640s) "one with regard for spiritual things." Related Spiritualistic.
Every two or three years the Americans have a paroxysm of humbug — ... at the present time it is Spiritual-ism. [J.Dix, "Transatlantic Tracings," 1853]