Kassius is a modern spelling of Cassius, an ancient Roman family name of uncertain meaning, usually linked to the Latin cassus, "empty" or "hollow". Cassius was one of Caesar's assassins in Shakespeare, and in America the name belonged to the boxer Cassius Clay before he became Muhammad Ali. The K spelling was too rare to be recorded in 2000; it climbed to number 1463 in 2022 and stood at number 2243 among US boys in 2025.