Shabbat (apart from meaning "rest") is also generally accepted as deriving from the Hebrew word for "seven", which is "sheva". And Shabbat is sometimes referred to in Hebrew as "yom shvi-i" ("seventh day").

Citation needed.

Klein Dictionary gives the etymology of שַׁבָּת as derived from שׁבת (to rest). I also found references suggesting the origin is with the Akkadian šapattum, the 15th of the month, but none related to שׁבע (which originates in Proto-Canaanite).

היּוֹם הַשְּׁבִיעִי (note the definite form!) is how Saturday is referred to in Genesis 2:2-3, without actually having the name שַׁבָּת. There's a some discussion about why שַׁבָּת isn't mentioned there as a name for the day, but regardless, your comment is the first time I read of the etymology of שַׁבָּת deriving from שׁבע.

I know it's not a reliable source by itself, and it lists no citations for the sentence in question, but FWIW, I based my answer on https://en.wikipedia.org/wiki/Shabbat#Etymology :

> Other related words are ... to sheva (שֶׁבַע) meaning seven, as Shabbat is the seventh day of the week ...

Trying to read this on Android (in Materialistic) was fascinating, each line containing a Hebrew (?) word caused some of the words around it to switch places, but the words themselves are fine??

Unicode TR-9 is a hard beast to tame.

In Portuguese, Monday through Friday translates to something like “Second Fair” through “Sixth Fair”¹. Saturday and Sunday aren’t numbered.

¹ “Fair” as in “a gathering of stalls and amusements for public entertainment”.

Similar in Arabic, except Friday is juma and Saturday is sabat.