• The ancient Greek word "ἑπτά" ≈ "seven" and is the source of English words such as "heptagon".
• The modern Greek word "επτά" (eh-PTA) ≈ "seven".

The English word "seven" goes back the PIE root "*SEPTM" ≈ "seven".

• The Middle English word "seuene" ≈ "seven".
• The Old English word "seofon" ≈ "seven"

• The Latin word "septem" ≈ "seven" from which we get the month name of "September", named for the seventh month when the first month of the Roman year was March.
• The French word "sept" ≈ "seven".
• The Spanish word "siete" ≈ "seven".
• The German word "sieben" ≈ "seven".

• The Old Church Slavonic word "седмь" ≈ "seven".
• The Russian word "семь" (sem) ≈ "seven".
• The Sanskrit word "सप्त" (sapta) ≈ "seven".
• The Hindi word "सात" (sa-at) ≈ "seven".

• The Roman numerals for seven are VII.
• The Arabic numeral for seven is 7.
• The binary representation of seven is 111.

The Hebrew word "שבוצ" (shee-ba) ≈ "seven" is synonymous with "week".

• Lev 23:15
• Deut 16:9
• Dan 9:26
• Dan 10:2

From where did the seven day week originate?

The Biblical answer is as follows.

The number seven is known in Bible terms as being a number of completeness or perfection.

The English word "perfect" often means without blemish or defect, although the "perfect" tense in linguistics is a tense that shows completion of something (e.g., in time).

The meaning sense in the Bible is that of completeness and not necessarily without error or defect.

The Greeks use the word for "seventh" to also refer to a group of "seven", such as a week, seven years, etc.

• The ancient Greek word "ἑβδομάς" ≈ "group of seven, week, seven years".
• The Latin word "hebdomas" ≈ "seven days, week, seventh day" is from the ancient Greek.
• long form: The modern Greek word "εβδομάδα" (eh-vtho-MA-tha) ≈ "week".
• short form: The modern Greek word "βδομάδα" (vtho-MA-tha) ≈ "week".

This idea was also used Hebrew.

The Hebrew word "יום" (yo-wm) ≈ "day".
Note: The end of the verse "God created and made" in Hebrew forms the basis for their word for "truth" as a reality (a future topic). Note that applying our present day concept of both "day" and "time" to the seven "days" of Creation relies on many assumptions that may or may not be valid and may not be relevant to any theological considerations.

The only important theological consideration appears to be that Adam and Eve were the first (and only) humans created and that they sinned before any children were produced. As for the apparent age of the universe in terms of "days", most disagreements are between the approximately 6,000 year literal Biblical view and the contemporary evolutionary science view of about 15 billion, or 15,000,000,000 years. From a (coded) information viewpoint, it does not matter how many years are involved. The (coded) information required could not arise (evolve) by chance so there is no need to jerry-rig Biblical arguments in order to support an arbitrary contemporary evolutionary science view that itself would not do what is required.

Back to the counting of the days and the week.

So the first day of the week is Sunday and the seventh day of the week is Saturday, accounting for the Jewish tradition that the day starts the evening before (as did Germanic days). Thus, Christmas Eve is the Christmas Evening or evening before. Same for All Hallowed Evening or Halloween.

The Germanic origin of days originating with the night is preserved in the English word "fortnight" as "fourteen night".

The English word "week" is from the Middle English word "weke" ≈ "week" which is from the Old English word "wice" ≈ "week" or the Old English word "wuca" ≈ "week".

The English word "week" is from the PIE root "*WEYG" ≈ "to bend, wind, turn, yield".

The English "week" then involves a "change" (to the new week).

The English word "week" is related to the Gothic word "wikon" ≈ "change" and involved a "turn" for (pagan) temple service.

This Gothic word is found in Luke 1:8 used to translate the modern Greek word "τάξει" (TA-ksee) ≈ "order" and from which we get the English word "taxonomy". The sense of "order" here is the change in order.

The German word "Woche" ≈ "week".

Wycliffe appears to have used the word "woke" long before the English usage in 2021.

In Galatians 2:5, the KJV (King James Version) translates The related ancient Greek word "εἴκω" (ee-ko) ≈ "yield, turn" as "yield" as in "give way" or "turn" as in "gave place".

The related Sanskrit word "विष्टी" (visti) ≈ "changing".

The GNT (Greek New Testament), Latin Vulgate, Gothic and Old Church Slavonic retain the "Sabbath" as the "week".

The Russian word "неделя" (ne-del-ya) ≈ "week" originates in the Old East Slavic word for Sunday that literally means "not working" or "day of rest". Since the word now means "week", there are Russian joke about "not working" during the week.

The Russian word "воскресенье" (vos-cre-shen-ya) ≈ "Sunday" and means "resurrection day". The Russian word "Суббота" (su-ba-ta) ≈ "Saturday" and means "Sabbath".

The modern Greek word "Κυριακή" (Kee-ree-a-KEE) ≈ "Sunday" and means "Lord's Day" for which the non-Biblical explanation is "main day".

The Latin word "Dominica" ≈ "Sunday" and means "Lord's Day".

The English word "Sunday" comes from the day of the "sun" but in Biblical terms is sometimes morphed into the day of the "son" (e.g., Jesus).

A non-Biblical inclination would be to make another day, say Monday, the first day of the week and Sunday the last day of the week.

Interesting question: (future topic, if I can find information on it)

• What civilizations did not use a seven day week?

The (atheistic) French Revolution attempt attempted to use a 10 day week and it did not work well. This was done from 1793 until 1802 and for a few weeks in 1871.

See Wikipedia for more on other calendars. https://en.wikipedia.org/wiki/Week (as of 2021-02-17).

In Old English, the Sabbath was known as the Old English word "raeste daigen" ≈ "rest day, Sabbath".