In Old English, the word for "Wednesday" was Wodnesdaeg, which literally meant "Woden's day." It comes from a loan translation of the Latin dies mercurii, which literally meant "day of Mercury," because Woden was the Germanic god associated with the Roman god mercury. This much is for certain. But how did the /o/ in Wodnesdaeg shift to the /e/ in "Wednesday?" This is a bit of a linguistic mystery, and we discuss some of the possibilities.