conjurer (n.)

late 14c., coniuracioun, "conspiracy, a plot, act of plotting" (senses now obsolete), also "a calling upon something supernatural, act of invoking by a sacred name, invocation of spirits, magic spell or charm," from Old French conjuracion "spell, incantation, formula used in exorcism" and directly from Latin coniurationem (nominative coniuratio) "a swearing together, conspiracy," in Medieval Latin "enchantment," noun of action from past-participle stem of coniurare "to swear together; conspire," from assimilated form of com "with, together" (see con-) + iurare "to swear," from ius (genitive iuris) "law, an oath" (see jurist).