mith·ri·date 
(mĭthrĭ-dāt′)
(mĭthrĭ-dāt′)n.
An antidote against poison, especially a confection formerly held to be an antidote to all poisons.
[Medieval Latin mithridātum, alteration of Late Latin mithridātīum, from Latin, neuter of Mithridātīus, of Mithridates, from Greek mithridāteios, after Mithridates VI, who is said to have acquired tolerance for poison.]