Like some of the names for months, our names for days of the week come largely from those of pagan gods. But the gods we chose to honor with our day names are not the Roman deities but the Germanic-Norse ones. The names for Tuesday through Friday are derivations of Tyrs’s day, (W)odin’s day, Thor’s day and Frigg’s day. Sunday and Monday are much simpler—they are named after the two heavenly bodies we have always with us, the sun and the moon.
The exception is Saturday whose name originated from the Roman god Saturn.
The names we use for the days of the week and the months of the year are relics of the origin of our language, English. Although Latin and the French influenced our language, English originated from Anglo-Frisian dialects brought to Britain in the mid fifth to seventh centuries AD by Anglo-Saxon migrants from what is now northwest Germany, southern Denmark and the Netherlands. Before that, the common language was Celtic that still survives as Gaelic in parts of Wales, Scotland, and Ireland. Dozens of words still used in modern English come from Gaelic, including pet, slogan, trousers, whiskey, and smidgeon.
The language we speak daily and pay no attention to is nevertheless laden with the history. It tells us where we came from and who we are.