Latin Meaning: The name Cassius is a Latin baby name. In Latin the meaning of the name Cassius is: Narcissistic; vain. American Meaning: The name Cassius is an American baby name.In American the meaning of the name Cassius is: Narcissistic; vain.Shakespearean Meaning: The name Cassius is a Shakespearean baby name.atin Meaning: The name Cassius is a Latin baby name. In Latin the meaning of the name Cassius is: Narcissistic; vain. American Meaning: The name Cassius is an American baby name. In American the meaning of the name Cassius is: Narcissistic; vain. Shakespearean Meaning: The name Cassius is a Shakespearean baby name.