Mithridate \MITH-ri-deyt\ , noun;
1. A confection believed to contain an antidote to every poison
According to the Oxford English Dictionary, this word entered English via Middle French and Latin, but it really comes from Hellenistic Greek as the name of Mithridates VI, king of Pontus, who was said to have made himself immune to poisons because of his constant use of antidotes.
Mithridates VI ruled Pontus from about 120 BC until his death in 63 BC and is remembered as one of the Roman Empire's most formidable and successful enemies. Oddly enough, this man who took extraordinary measures to make himself immune to poisons tried to commit suicide by poison after he was defeated and felt himself in danger of capture by Romans. It didn't work, of course, and he was killed with a sword.
*Today's word and the first definition were both taken from Dictionary.com's 'Word of the Day' for Tuesday, November 23