Zosima’s name day is April 4, the feast of Zosimas of Palestine.
Churches that follow the Old (Julian) Calendar keep the same feast on April 17 of the civil calendar. See everything commemorated on April 4.
The saint behind the name
Zosimas of Palestine
April 4, Venerable, Ζωσιμάς
Zosimas entered the monastic life as a child and lived for many decades in a monastery of Palestine before moving to a community near the Jordan. Going into the desert during Great Lent, as was the custom there, he met the ascetic Mary of Egypt and heard from her the story of her repentance.
Also celebrating on April 4
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.