Themis’s name day is December 21, the feast of Themistocles of Myra.
Churches that follow the Old (Julian) Calendar keep the same feast on January 3 of the civil calendar. See everything commemorated on December 21.
The saint behind the name
Themistocles of Myra
December 21, Martyr, Θεμιστοκλής
The holy martyr Themistocles was a shepherd of Myra in Lycia who suffered under the persecution of Decius in the third century. Tradition relates that when soldiers searched for a Christian named Dioscorides, Themistocles refused to betray him and declared himself a Christian instead.
Name days: Themistoklis, Themistocles, Themis
Also celebrating on December 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.