mithridate (n.)

in old pharmacology, "a compound of many ingredients regarded as a universal antidote against poison," from Medieval Latin mithridatum, from Late Latin mithridatium, neuter of Mithridatius "pertaining to Mithridates VI" (Greek Mithridatēs, from Old Persian, literally "gift of Mithra"), king of Pontus in 1c. B.C.E., who made himself poison-proof by taking small doses of the usual poisons.