The Collaborative International Dictionary of English v.0.48:

Pyrrhonism \Pyr"rho*nism\, n. [From Pyrrho, the founder of a
   school of skeptics in Greece (about 300 b. c.): cf. F.
   pyrrhonisme.]
   Skepticism; universal doubt.
   [1913 Webster]

The Devil's Dictionary (1881-1906):

PYRRHONISM, n.  An ancient philosophy, named for its inventor.  It
consisted of an absolute disbelief in everything but Pyrrhonism.  Its
modern professors have added that.