Origins
Wednesday is Odin's day, and its spelling — with that famously silent 'd' — preserves the name of the most complex and powerful deity in the Germanic pantheon, hidden in plain sight within an everyday word that most English speakers pronounce without ever suspecting its mythological cargo.
The word derives from Old English 'wōdnesdæg,' a compound of the genitive 'wōdnes' (of Wōden) and 'dæg' (day). This was a calque of Latin 'Mercuriī diēs' (day of Mercury), with the Germanic god Wōden substituted for the Roman god Mercury through interpretatio germanica. The equation of Wōden with Mercury, rather than with Jupiter or any other Roman deity, reveals much about how the Germanic peoples understood their own chief god. While Jupiter was associated primarily with sky, thunder, and sovereignty, Mercury was the god of wisdom, eloquence, travel, commerce, and the guidance of souls to the underworld. These were precisely the attributes most strongly associated with Wōden/Odin in Germanic tradition: the wandering god of poetry, runes, secret knowledge, and death.
The name Wōden itself comes from Proto-Germanic *Wōdanaz, derived from *wōdaz, meaning 'inspired,' 'frenzied,' or 'possessed.' This traces to the PIE root *wāt- (to blow, to inspire), which also produced Latin 'vātēs' (prophet, seer) and Old Irish 'fáith' (seer, prophet). The name thus characterizes Odin as the god of ecstatic inspiration — the frenzied wisdom that comes through self-sacrifice, shamanic trance, and the drinking of the mead of poetry.
Middle English
The phonological reduction from 'wōdnesdæg' to 'Wednesday' (/ˈwɛnz.deɪ/) is one of the most dramatic in English. The cluster /dn/ in 'Wōdnes-' was simplified by dropping the /d/, a change that occurred gradually during the Middle English period. The spelling, however, was already fixed by scribal convention and was never updated to match the pronunciation. This makes 'Wednesday' one of English's most cited examples of a word whose spelling preserves historical phonology that the spoken language has long since abandoned.
The cognate forms across Germanic languages show interesting variation. Dutch 'woensdag' preserves Wōden transparently. The Scandinavian languages — Swedish 'onsdag,' Danish 'onsdag,' Norwegian 'onsdag' — use forms derived from Old Norse 'óðinsdagr,' with the initial 'w' lost as part of a regular sound change in North Germanic. Most striking is German 'Mittwoch' (mid-week), which replaced the pagan name entirely. This substitution was driven by Christian missionaries — particularly Boniface in the eighth century — who specifically targeted 'Wōdanaz' as the most dangerous of the pagan gods and sought to eliminate his name from everyday speech. The success of this campaign in German (and the failure of similar efforts in English, Dutch, and Scandinavian) is one of the curiosities of European linguistic history.
In the Romance languages, the Latin 'Mercuriī diēs' produced French 'mercredi,' Spanish 'miércoles,' Italian 'mercoledì,' and Romanian 'miercuri' — all transparently preserving Mercury. Portuguese 'quarta-feira' (fourth fair/day) is again the exception, reflecting the ecclesiastical numbering system adopted in Portuguese.
Latin Roots
The cultural association of Wednesday with the middle of the week is strong in many traditions. The German 'Mittwoch' makes this explicit. In English, the informal 'hump day' — referring to the midpoint of the working week — captures the same idea. Yet in the original Roman planetary system, Wednesday was not the middle of the week at all; the week began with Saturday (Saturn's day), making Wednesday the fifth day.
Odin's association with Wednesday has had a modest cultural afterlife. In Neil Gaiman's novel 'American Gods,' the character Mr. Wednesday is a thinly veiled Odin, and his name is a direct reference to this etymological connection. The character explicitly explains his name as 'Wōden's day' in the narrative, bringing the buried mythology back to the surface for modern readers.