Dies Dominicus

Dies Dominicus (ἡ κυριακή), the ancient name of the Lord's Day, which was also called Sunday, dies solis, especially when, in addressing the heathen, it was necessary to distinguish the day. During the early ages it was never called the Sabbath, that word being confined to the seventh day of the week, which continued to be observed by the Jews, and in part also, for a short time, by some of the converts to Christianity. — Bingham, Orig. Eccles. bk. 20, ch. 2, § 1; Coleman, Ancient Christianity, ch. 48, § 2.