Quick answer
Cassius is a boy name meaning "empty, vain".
Pronunciation: Latin /ˈkas.si.us/; English /ˈkæʃ.əs/; English /ˈkæs.i.əs/.
Meaning and history
Roman family name that was possibly derived from Latin cassus meaning "empty, vain". Lucius Cassius Dio was a 3rd-century Roman historian. This name was also borne by several early saints. In modern times, it was the original first name of boxer Muhammad Ali (1942-2016), who was named after his father Cassius Clay, who was himself named after the American abolitionist Cassius Clay (1810-1903).
Notes and context
Usage: ancient roman