The Collaborative International Dictionary of English v.0.48:

Cassius \Cas"sius\, n. [From the name of the discoverer, A.
   Cassius, a German physician of the 17th centry.]
   A brownish purple pigment, obtained by the action of some
   compounds of tin upon certain salts of gold. It is used in
   painting and staining porcelain and glass to give a beautiful
   purple color. Commonly called Purple of Cassius.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Cassius
    n 1: prime mover in the conspiracy against Julius Caesar (died
         in 42 BC) [syn: Cassius, Cassius Longinus, Gaius
         Cassius Longinus]