The name Cassian is a boy's name of Latin origin meaning "hollow". Cassian and is often added to lists like Unique Boy Names: Unusual and Rare and discussed in our forums with posts like "Rate the Previous Signature!".
From the experts:
Cassian is a saints' and Latin clan name, related to Cassius, that is virtually unused and waiting to be discovered.
There have been at least four fourth and fifth century St. Cassians, one of whom is the patron saint of (not many of them left) stenographers. John Cassian was a monk and ascetic writer who introduced Eastern monasticism into the West.
Patrick Wilson used the alternate spelling Kassian for his son.