There is a distinction. YHVH marked the Seventh Day with the name Shabbat, but He did not mark any other day with a name but only with numbers. Because the Shabbat is His Holy Day Forever and a sign that He is The God of Israel, The Creator, all who love The Creator would worship Him on that day and not replace it with the First day of the Week, calling it Sunday or the day when the sun-god is worshiped.