Where does “ευθήρια” come from?

ευθήρια (Greek) comes from Translingual Eutheria, from Ancient Greek εὖ, from Ancient Greek ἐΰς, from Proto-Hellenic ehu-, from Proto-Indo-European h₁su-, from Proto-Indo-European h₁wes- — good; to be cheerful, happy; to eat, to feast.

ευθήρια (Greek): The Eutheria