Þūnresdæg

The Romans called it dies Iovis, the day of Jupiter. Jupiter was the king of the gods, the sky-father, the one who threw thunderbolts when he was angry. His Greek equivalent was Zeus. His day was the fifth in the planetary week. French jeudi (from Jovis dies), Spanish jueves, Italian giovedi -- Jupiter still holds the day across Romance Europe.

The Germanic peoples swapped in Thor, the red-bearded thunder god of Norse mythology. The match was straightforward: both Jupiter and Thor controlled thunder and lightning. Both were the strongest gods in their respective pantheons. Old English Thunresdaeg literally meant 'Thunder's day.' Old Norse had Thorsdagr. The equation Jupiter = Thor was one of the cleanest in the whole interpretatio germanica.

Thor was Odin's son in the Norse myths, a god more popular with ordinary people than his father. While Odin was the god of kings, poets, and the dead, Thor was the god of farmers, travelers, and anyone who needed rain. His hammer Mjolnir was the most famous weapon in Norse mythology. Adam of Bremen, writing around 1070 CE, recorded that Thor's statue held the central position in the temple at Uppsala, Sweden -- above even Odin's.

German Donnerstag ('thunder-day') keeps the thunder but drops the god's name. English Thursday keeps the god but obscured his identity: most English speakers do not hear 'Thor' in 'Thursday' without being told. The Marvel Cinematic Universe, starting with Thor in 2011, may have done more to reconnect the day with its god than any linguistic education in the last five centuries.