Cassian is the English form of the Latin Cassianus, from the Roman family name Cassius, whose meaning is uncertain and sometimes explained as "empty" or "vain". Saint John Cassian was a 5th-century monk who shaped Western monasticism, and the rebel spy Cassian Andor from Rogue One and the series Andor gave the name a modern hero. Cassian was almost unused in the United States until 2017; it entered the top 1000 in 2021 and ranks number 479 in 2025, its best rank so far.