In many languages of the world, the names of the days of the week are derived from the names of planets, gods or numeric values.
Sunday from old English comes from the Latin Dies solis, which means “Sun’s day”. Later came the ecclesiastic Dies Dominica, i.e. the day of the Lord, which evolved in many Romance languages: domingo (in Spanish and Portuguese), dimanche (in French), duminică (in Romanian), domenica (in Italian).
The first day of the week in old English is the day of the Moon (Moon day → Monday). This was translated from the Latin Dies Lunae. Lundi (in French), lunes (in Spanish), luni (in Romanian), lunedi (in Italian) appeared later.
The correspondent for Tuesday in old English was Tyr’s day. Tyr was an ancient god of war and heroic glory in pagan Norse mythology, assimilated by Germanic peoples with the penetration of the northern peoples into the center of Europe. In Latin there is Dies Martis (Mars’ day), who was the Roman god of war. Then appeared mardi (in French), martes (in Spanish), marţi (in Romanian), martedi (in Italian).
The name Wednesday has the same Germanic origin, which comes from the name of the Norse god Wodan or Odin, worshiped not only by northern peoples, but also by Anglo-Saxons until the 7th century. Dies Mercurii (Mercury’s Day) comes from Latin and gives birth to mercredi (in French), miércoles (in Spanish), miercuri (in Romanian), mercoledi (in Italian). The correspondence between Mercury and Odin as deities is that they both led the spirits into corresponding mythologies. At the same time, in German, Wednesday is Mittwoch, meaning mid-week.
Thursday comes from the Latin Dies Iovis (Jupiter’s day), transformed into jueves in Spanish, giovedi in Italian, jeudi in French. In modern English, Thursday comes from the name Thor, the god of thunder in Norse mythology.
Friggo is the name of the German goddess of beauty and Freya is the goddess of beauty in the Norse mythology, both having the modern correspondent in English – Friday. Dies Veneris (Venus’s day) from Latin generated vendredi (in French), viernes (in Spanish), venerdi (in Italian) and vineri (in Romanian).