Leonides’s name day is April 15, the feast of Leonides of Athens.
Churches that follow the Old (Julian) Calendar keep the same feast on April 28 of the civil calendar. See everything commemorated on April 15.
The saint behind the name
Leonides of Athens
April 15, Hierarch, Λεωνίδης Αθηνών
Leonides was Bishop of Athens in the third century. During the persecution of Decius he was arrested and taken to Corinth, where he was tried with seven Christian women who had been converted by his preaching.
Also celebrating on April 15
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.