What does "mithridate" mean?

Mithridate: An antidote against poison, or a composition in form of an electuary, supposed to serve either as a remedy or a preservative against poison; an alexipharmic; -- so called from King Mithridates, its reputed inventor. [Love is] a drop of the true elixir; no mithridate so effectual against the infection of vice. Southey.