Days of the Week

The concept of the week first appears in Greek in the translation of the Septuagint. Augustus adopted the seven-day Hebrew week as a unit of time, replacing the older eight-day Roman unit of time known as nūndinae in the plural (the term literally means "one-day", nōnus diēs).

The week consists of 7 days and Shabbat is a day of rest and prayer. Each day begins and ends at sunset, not at midnight as in the Gregorian calendar, and ends at the same time the next day.

The Jews are the first people to use the week as a cyclically repeating unit of time of seven days and it has been established since at least the 5th century BC.

The central day of the Jewish week is the Sabbath and the other days are named after their relative position to the Sabbath:

Sunday for Jews is yóm rishón = "the first day (after the Sabbath)"

Friday in Hebrew is known as the Sixth Day (yóm shishí, this name survives in the Ibero-Romance descendants of the Latin feria sexta = "Friday", e.g. Portuguese sexta-feira) or Erev Shabbat (the evening before Shabbat, the eve of Shabbat). Because the evening before Shabbat begins the process of preparation/preparation for Shabbat, Greek-speaking Jews coined the term Friday for the day before Shabbat.

The calendar names Monday, Tuesday, Wednesday, Thursday are translations of the Hebrew calendar names (yóm shení = "the second day (after Saturday) > Monday, etc.).