Kassianos’s name day is May 21, the feast of Kassianos the Greek.
Churches that follow the Old (Julian) Calendar keep the same feast on June 3 of the civil calendar. See everything commemorated on May 21.
The saint behind the name
Kassianos the Greek
May 21, Venerable, Κασσιανός ο Έλληνας
Kassianos was a Greek nobleman named Constantine who came to Moscow in the entourage of Sophia Palaiologina. He became a monk at the Ferapontov Monastery and later founded a monastery near Uglich on the Volga.
Also celebrating on May 21
These names share the feast, many of them other forms of the same name:
What to say on a name day
The Greek wish is Χρόνια Πολλά (Chronia Polla), “many years.” A call or a short message on the day is what people remember. See name day wishes you can send and what a name day is.