Cassius /cas-sius/ [3 sylls.] as a boys' name is pronounced KASH-us. It is of Latin origin. Possibly empty, hollow. An old Roman family clan name.resented below is the baby name popularity of Cassius for boys. Cassius reached its highest position of #684 in the U.S. in the 1880s, and is at #704 currently. (2014 Birth Statistics).