The Spanish word 'miércoles' (meaning 'Wednesday') comes from the Latin 'dies Mercurii', which literally meant 'day of Mercury'. Mercury was an important Roman god (known as 'Mercurius' in Latin) associated with commerce, communication, and travel. The name evolved through Vulgar Latin 'mercuris', then to Old Spanish 'miercores', before reaching its modern Spanish form 'miércoles'.

This naming pattern for Wednesday as 'Mercury's day' is actually common across many European languages, similar to how English 'Wednesday' comes from 'Woden's day' (Woden being the Germanic equivalent of Mercury).

The Spanish word 'mercado' (market) and 'mercantil' (mercantile) are related words that also trace back to Mercury, as he was the god of commerce and trade. While 'miércoles' preserved Mercury's name in reference to the day of the week, these related words maintained the connection to Mercury's role as patron of merchants and commerce.

Several English words share this connection to Mercury, including 'mercury' (both the planet and the metallic element), 'mercurial' (meaning changeable in temperament, like the swift-moving god), and 'merchant' (from Mercury's role as god of commerce). While these words took on different meanings than the Spanish 'miércoles', they all trace back to the same Roman god Mercurius.