Κυριακή (Byzantine Greek) comes from Ancient Greek ἡ Κυριακὴ ἡμέρα, from Ancient Greek κυριακή, from Ancient Greek Κυριακός, from Ancient Greek -ακός, from Ancient Greek -κός, from Proto-Indo-European -ḱos — -y, -ic.
Κυριακή (Byzantine Greek): Sunday; Sunday, Lord's Day