The days of the week have been named after the seven planets of classical astronomy, since the Roman period. They are also numbered, beginning at Sunday, Monday or Saturday depending on the society and tradition.
The Germanic peoples adapted the system introduced by the Romans but glossed their indigenous gods over the Roman deities (with the exception of Saturday) in a process known as Interpretatio germanica. The date of the introduction of this system is not known exactly, but it must have happened later than AD 200 but before the introduction of Christianity during the 6th to 7th centuries, i.e., during the final phase or soon after the collapse of the Western Roman Empire. This period is later than the Common Germanic stage, but still during the phase of undifferentiated West Germanic. The names of the days of the week in North Germanic languages were not calqued from Latin directly, but taken from the West Germanic names.
Sunday: Old English Sunnandæg, meaning "sun's day." This is a translation of the Latin phrase dies Solis. English, like most of the Germanic languages, preserves the original pagan/sun associations of the day. Many other European languages, including all of the Romance languages, have changed its name to the equivalent of "the Lord's day" (based on Ecclesiastical Latin dies Dominica). In both West Germanic and North Germanic mythology the Sun is personified as a goddess, Sunna/Sól.
Monday: Old English Mōnandæg, meaning "Moon's day." This is based on a translation of the Latin name dies lunae. In North Germanic mythology, the Moon is personified as a god, Máni.
Tuesday: Old English Tīwesdæg, meaning "Tiw's day." Tiw (Norse Týr) was a one-handed god associated with single combat and pledges in Norse mythology and also attested prominently in wider Germanic paganism. The name of the day is based on Latin dies Martis, "Day of Mars".
Wednesday: Old English Wōdnesdæg meaning the day of the Germanic god Wodan (known as Óðinn among the North Germanic peoples), and a prominent god of the Anglo-Saxons (and other Germanic peoples) in England until about the seventh century. It is based on Latin dies Mercurii, "Day of Mercury." The connection between Mercury and Odin is more strained than the other syncretic connections[citation needed]. The usual explanation is that both Wodan and Mercury were considered psychopomps, or guides of souls after death, in their respective mythologies; both are also associated with poetic and musical inspiration.
Thursday: Old English Þūnresdæg, meaning 'Þunor's day'. Þunor means thunder or its personification, the Norse god known in Modern English as Thor. Similarly Dutch donderdag, German Donnerstag ('thunder's day') and Scandinavian Torsdag ('Thor's day'). Thor's day corresponds to Latin dies Iovis, "day of Jupiter".
Friday: Old English Frīgedæg, meaning the day of the Norse goddess Frígg. The Norse name for the planet Venus was Friggjarstjarna, 'Frigg's star'. It is based on the Latin dies Veneris, "Day of Venus."
Saturday: the only day of the week to retain its Roman origin in English, named after the Roman god Saturn associated with the Titan Cronus, father of Zeus and many Olympians. Its original Anglo-Saxon rendering was Sæturnesdæg. In Latin it was dies Saturni, "Day of Saturn." The Scandinavian Lørdag/Lördag deviates significantly as it has no reference to either the Norse or the Roman pantheon; it derives from old Norse laugardagr, literally "washing-day." The German Sonnabend and the Low German words Sünnavend mean the "evening before Sunday", the German word Samstag derives from the name for Shabbat.
