Names of the days of the week

The history of the seven-day week can be traced to ancient civilizations. Sunday remained the first day of the week, being considered the day of the sun god Sol Invictus and the Lord's Day, while the Jewish Sabbath remained the seventh. Most historians agree the seven-day week dates back to Babylonians who started using it about 4,000 years ago. The number 7 was sacred to the Babylonians. Emperor Constantine of the Roman Empire made the Day of the Sun (dies Solis, "Sunday") a legal holiday centuries later.

In the international standard ISO 8601, Monday is treated as the first day of the week, but in many countries it is counted as the second day of the week.

Days named after planets

Greco-Roman tradition

Between the first and third centuries CE, the Roman Empire gradually replaced the eight-day Roman nundinal cycle with the seven-day week. The earliest evidence for this new system is a Pompeiian graffito referring to 6 February (ante diem viii idus Februarias) of the year 60 CE as dies solis ("Sunday"). Another early witness is a reference to a lost treatise by Plutarch, written in about 100 CE, which addressed the question of: "Why are the days named after the planets reckoned in a different order from the 'actual' order?" The treatise is lost, but the answer to the question is known; see planetary hours.

The Ptolemaic system of planetary spheres asserts that the order of the heavenly bodies from the farthest to the closest to the Earth is Saturn, Jupiter, Mars, Sun, Venus, Mercury, and the Moon; objectively, the planets are ordered from slowest to fastest moving as they appear in the night sky.

The days were named after the classical planets of Hellenistic astrology, in the order: Sun (Helios), Moon (Selene), Mars (Ares), Mercury (Hermes), Jupiter (Zeus), Venus (Aphrodite), and Saturn (Cronus).

The seven-day week spread throughout the Roman Empire in late antiquity.By the fourth century CE, it was in wide use throughout the Empire.

The Greek and Latin names are as follows:

Romance languages

Except for in Portuguese and Mirandese, the Romance languages preserved the Latin names, except for the names of Sunday, which was replaced by [dies] Dominicus (Dominica), that is, "the Lord's Day", and of Saturday, which was named for the Jewish Sabbath. Mirandese and Portuguese use numbered weekdays, but retain sábado and demingo/domingo for weekends. Meanwhile, Galician occasionally uses them alongside the traditional Latin-derived names, albeit to a lesser extent (see below).

Celtic languages

Early Old Irish adopted the names from Latin, but introduced separate terms of Norse origin for Wednesday, Thursday and Friday, then later supplanted these with terms relating to church fasting practices.

In Welsh, the word for ‘day’ dydd is replaced by the words for ‘morning' bore, ’night’ nos or ‘afternoon’ prynhawn, etc to say ‘Monday morning’ bore Llun, or ‘Friday night’ nos Wener, etc. It is never *nos dydd Llun or *bore dydd Llun which are ungrammatical.

Albanian language

Albanian adopted the Latin terms for Tuesday, Wednesday and Saturday, translated the Latin terms for Sunday and Monday using the native names of Diell and Hënë, respectively, and replaced the Latin terms for Thursday and Friday with the equivalent native deity names Enji and Prende, respectively.

Adoptions from Romance

Other languages adopted the week together with the Latin (Romance) names for the days of the week in the colonial period. Several constructed languages also adopted the Latin terminology.

With the exception of sabato, the Esperanto names are all from French, cf. French dimanche, lundi, mardi, mercredi, jeudi, vendredi.

Germanic tradition

The Germanic peoples adapted the system introduced by the Romans by substituting the Germanic deities for the Roman ones (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 100 AD 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 (pronounced ), meaning "sun's day". This is a translation of the Latin phrase diēs Sōlis. English, like most of the Germanic languages, preserves the day's association with the sun. 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 Sunna/Sól.
• Monday: Old English Mōnandæg (pronounced ), meaning "Moon's day". This is equivalent to the Latin name diēs Lūnae. In North Germanic mythology, the Moon is personified as Máni.
• Tuesday: Old English Tīwesdæg (pronounced ), 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 also related to the Latin name diēs Mārtis, "Day of Mars" (the Roman god of war).
• Wednesday: Old English Wōdnesdæg (pronounced ) meaning the day of the Germanic god Woden (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. This corresponds to the Latin counterpart diēs Mercuriī, "Day of Mercury", as both are deities of magic and knowledge. Importantly, both are also psychopomps, carrying the souls of the dead to the afterlife. The German Mittwoch, the Low German Middeweek, the miðviku- in Icelandic miðvikudagur and the Finnish keskiviikko all mean "mid-week".
• Thursday: Old English Þūnresdæg (pronounced ), 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'), Finnish torstai, and Scandinavian torsdag ('Thor's day'). "Thor's day" corresponds to Latin diēs Iovis, "day of Jupiter" (the Roman god of thunder).
• Friday: Old English Frīgedæg (pronounced ), meaning the day of the Anglo-Saxon goddess Frīg. The Norse name for the planet Venus was Friggjarstjarna, 'Frigg's star'. It is based on the Latin diēs Veneris, "Day of Venus".
• Saturday: named after the Roman god Saturn associated with the Titan Cronus, father of Zeus and many Olympians. Its original Anglo-Saxon rendering was Sæturnesdæg (pronounced ). In Latin, it was diēs Sāturnī, "Day of Saturn". The Nordic laugardagur, leygardagur, laurdag, etc. deviate significantly as they have no reference to either the Norse or the Roman pantheon; they derive from Old Nordic laugardagr, literally "washing-day". The German Sonnabend (mainly used in northern and eastern Germany) and the Low German Sünnavend mean "Sunday Eve"; the German word Samstag derives from the name for Shabbat.

Adoptions from Germanic

Sami languages have weekday names influenced from neighboring languages, with a majority of weekday names being from Germanic-Norse origin.

Hindu tradition

Hindu astrology uses the concept of days under the regency of a planet under the term vāsara/vāra, the days of the week being called sūrya-/ravi-/āditya, chandra-/soma-, maṅgala-, budha-, guru-/bṛhaspati-, śukra-, and śani-vāsara. śukrá is a name of Venus (regarded as a son of Bhṛgu); guru is here a title of Bṛhaspati, and hence of Jupiter; budha "Mercury" is regarded as a son of Soma, that is, the Moon. Knowledge of Greek astrology existed since about the 2nd century BC, but references to the vāsara occur somewhat later, during the Gupta period (Yājñavalkya Smṛti, c. 3rd to 5th century AD), that is, at roughly the same period or before the system was introduced in the Roman Empire.

In languages of the Indian subcontinent

Southeast Asian languages

The Southeast Asian tradition also uses the Hindu names of the days of the week. Hindu astrology adopted the concept of days under the regency of a planet under the term vāra, the days of the week being called āditya-, soma-, maṅgala-, budha-, guru-, śukra-, and śani-vāra. śukrá is a name of Venus (regarded as a son of Bhṛgu); guru is here a title of Bṛhaspati, and hence of Jupiter; budha "Mercury" is regarded as a son of Soma, that is, the Moon.

Northeast Asian languages

East Asian tradition

The East Asian naming system for the days of the week closely parallels that of the Latin system and is ordered after the "Seven Luminaries" (七曜 qī yào), which consists of the Sun, Moon and the five classical planets visible to the naked eye.

The Chinese had apparently adopted the seven-day week from the Hellenistic system by the 4th century AD, although by which route is not entirely clear. It was again transmitted to China in the 8th century AD by Manichaeans, via the country of Kang (a Central Asian polity near Samarkand). The 4th-century AD date, according to the Cihai encyclopedia, is due to a reference to Fan Ning (范寧), an astrologer of the Jin dynasty. The renewed adoption from Manichaeans in the 8th century AD (Tang dynasty) is documented with the writings of the Chinese Buddhist monk Yijing and the Ceylonese Buddhist monk Bu Kong.

The Chinese transliteration of the planetary system was soon brought to Japan by the Japanese monk Kobo Daishi; surviving diaries of the Japanese statesman Fujiwara no Michinaga show the seven-day system in use in Heian period Japan as early as 1007. In Japan, the seven-day system was kept in use (for astrological purposes) until its promotion to a full-fledged (Western-style) calendrical basis during the Meiji era. In China, with the founding of the Republic of China in 1911, Monday through Saturday in China are now named by their numbers, with Monday as "weekday 1" and Saturday as "weekday 6".

Pronunciations for Classical Chinese names are given in Standard Chinese.