In ancient Rome, the weekdays got their names from planets, the sun and the moon. Every day was dominated by its own planet and its divine power: the sun, the moon, Mars, Mercurius, Jupiter, Venus, Saturnus.
In the Germanic languages, these names were translated, all names of planets named after Roman gods received names after Germanic gods.
Note: The Norwegian system of writing and spelling differs from English in the way that capitals are not used for names of days, months and nationalities.
The day of the Moon (måne), translated from Latin lunae
Tyr's day: the Old Norse God of war
Old Norse: tysdagr / tyrsdagr
Latin: dies Martis
French: mardi, from the planet Mars
Odin's day: Odin was the most powerful God of all in the Norse mythology
Old Norse: Odinsdagr
Latin: dies Mercurii
French: mercredi, from the planet Mercurius
Thor's day: Thor was the second greatest God after Odin. He is mostly known for his hammer with which he made thunder and ligthning, and for his two birds, Hugin and Munin.
Old Norse: Thòrsdagr
Latin: dies Jovis
French: jeudi, from the planet Jupiter
The Roman love goddess Venus has her counterpart in the Nordic Freya; Old Norse Frigg and Freyja.
Old Norse: Frjâdagr
Latin: die Veneris
French: vendredi, from the planet Venus
Lørdag means "the day of the washing", the day of the week when people washed themselves! It was especially the hair they washed, in a special solution made out of lye of ashes (askelut) which made the hair yellowish or reddish. Laug means washingwater, and comes from 'lut' in 'askelut'.
Old Norse: laugardagr
Latin: Saturni dies
French: samedi, from the planet Saturnus, and also meaning "the day of the sabbath"
Lørdag is the only day which name does not derive from astrology nor foreign images.
'søn' comes from Old Norse sunna = sun.
Old Norse: dròttingsdagr, introduced with Christianity, related to Latin dies dominicus
Latin: dies solis
Latin: dies dominicus