Week designates generally a period of seven days. It was probably first instituted as a kind of broad subdivision of the periodical month, corresponding to the four quarters of the moon, or about 7 days. Neither this civil division of time nor its application to sacred things was originally solely Jewish, but we find the earliest Jewish cosmogony and legislation closely connected with it. The older of the two accounts of the creation (Gen. ii. 4 et seq.) does not recognise the six days' work, and indeed we may assume the connection between the seven days' week and the work of creation as an accommodating generalisation of later days with the symbolic number Seven (q.v.). The Sabbath is emphatically the day of rest, while seven weeks after the Passover the Pentecost or Feast of Weeks takes place. The Egyptians at an early period counted seven periodical days, naming them according to the seven planets. The application of the names of the planets to the days of the week in the order they now stand originated in this way: it was an astrological notion that each planet in order presided over an hour of the day, the order, according to their distances from the earth, being, on the geocentric system, Saturn, Jupiter, Mars, the Sun, Venus, Mercury, the Moon. Assuming Saturn to preside over the first hour of Saturday, and assigning to each succeeding hour a planet in order, the 22d hour will fall again to Saturn, the 23d to Jupiter, the 24th to Mars, and the first hour of the next day to the Sun; in the same way the first hour of the following day falls to the Moon, and so on. From Alexandria this seven days' week was imported, together with the names of the individual days, to the Greeks—who previously divided their months into three decades—and to the Romans about the time of Christ. Rome had previously counted her periods by eight days, the eighth day itself being originally called Nundinæ—a term later applied to the whole cycle—as returning nono quoque die, when the country-people were in the habit of coming to town for the purposes of business, and chiefly to inquire after public news, the changes in government and legislation, vacant places, and the like. But the seven days' cycle soon found great favour among the Romans, owing partly perhaps to the spread of Egyptian astrology, although the change was not officially introduced before Constantine. It is certain that the Jewish name Sabbath came into use in Rome, and from Rome it spread to all the Romance languages, and even into the Teutonic. In the same manner the Latin Septimana (the Greek hebdomas) has become the modern designation for week in the Italian Settimana, Spanish Semana, and French Semaine. The Codex Theodosianus is the first document which adopts the term Septimana in the meaning of 'week.' The Jews, as well as the early Christians, had no special names for the single days, but counted their number from the previous Sabbath, beginning with Sunday, as the first after the Sabbath, and ending with Friday, as the sixth after the previous or eve (Ereb) of the next Sabbath. After a very short time, however, young Christianity, which in the same manner had endeavoured to count from the feria secunda, or second day after Sunday, to the Septima (or Saturday), had to fall back again upon the old heathen names, previously introduced in Gaul, Germany, &c. by the heathen Romans. The Sunday, or dies Solis, alone was changed in many of the Romanic languages in accordance with the new creed. It was called Kyriake, dies Dominicus or Dominica, the 'Day of the Lord,' a term which in Italian became Domenica, in Spanish Domingo, and Dimanche in French. It is very curious to notice how the names of the five days of the week which followed those named after the sun and moon became Germanised, as it were, or the names of the originally imported gods translated into those of the Germanic divinities. Quakers disapprove of the heathen names, and name the days 'First Day,' 'Second Day,' &c. The Arabs, like the Jews, count their days, beginning and ending with sunset, by sevens, without giving them planetary names. Greeks, Slavs, and Finns also count their days from Sunday, instead of naming them. The French Revolution altered the seven days' week into a decade of ten days; but the new computation introduced in 1793 was abrogated again in 1805. The 'weeks of years,' in Hebrew prophetic poetry (like the Roman annorum hebdomadæ), indicate cycles of seven years.
See CALENDAR, SABBATH; and Ideler's Chronologie (1831); Grimm's Deutsche Mythologie (1835); and Lenormant's La Magie chez les Chaldéens (1874); and for the Feast of Weeks, see FESTIVALS.