Princess Bride What is the name of poison that killed Vizzini?

The poison that killed Vizzini in The Princess Bride was called "Iocane powder".

Vizzini believed he had cleverly outsmarted Westley by switching the goblets, but Westley had actually anticipated his move and switched the goblets back. The poison that was in the goblet that Vizzini chose was Iocane powder, which was fatal.