Of all the theophoric days of the week, Friday is the most controversial. Some assert that Friday is named after the Viking god Freyr. This makes sense because the 11th-century eyewitness, Adam of Bremen, describes Odin, Thor, and Freyr as forming a top-tier of gods that were often worshipped together (including at the magnificent temple at Uppsala). Freyr was a fertility god and god of plenty, and so the Vikings would probably not want to offend him by leaving him out.
Others believe that Friday is not named after Freyr but after his sister Freyja. Freyja was a goddess of war, magic, fertility, and erotic love. Still, others believe that the day is named after Frigg, Odin’s wife and the Queen of Asgard. The matter is further complicated: Freyja and Frigg have many overlapping characteristics and may have once even been the same goddess. This ambiguity has long roots, as Friday was called Frigesdaeg in some dialects but Freyjasdagr in Old Norse.
An important clue as to who the day really belongs to can be found by comparing it to the Roman model. For the Romans, the sixth day of the week was devoted to Venus, the goddess of love, beauty, and passion. If the comparison still holds, it would seem that Friday is, therefore, Freyja’s Day. We will probably never know for sure, and indeed perhaps our Viking ancestors honored all three on this day.