The story
Wednesday is "Woden's day". Woden was the chief god of the pagan Anglo-Saxons — the same figure the Norse called Odin and the Germans Wotan: a god of wisdom, poetry, magic and the dead. Old English speakers called the day Wōdnesdæg, and they said every letter of it: something like WOHD-nes-dai, D included.
The name is a translation. The Romans called this day Mercurii dies, "day of Mercury" — hence French mercredi and Spanish miércoles. Germanic speakers matched Mercury, the wise traveller who guided souls, with Woden, and put their own god in his place.
The spelling settled in Middle English as Wednesday, with the vowel already shifted from Wōd- to Wed-. Then speech kept moving and the spelling did not. The cluster d-n-s is awkward to say, so speakers simplified it: the D dropped out and the middle vowel disappeared. By the late Middle Ages the everyday pronunciation was already close to WENZ-day — three written syllables, two spoken ones. Printers, and later dictionaries, fixed the old spelling in place.
Woden is still hiding in English place names — Wednesbury in the English Midlands is "Woden's fort". Dutch keeps him more openly in woensdag. German avoided the pagan name altogether and says Mittwoch, "mid-week".
