

In Russian the days of the week are mostly numbers, e.g. Tuesday is the second day, so Tuesday is Вторник, which comes from второй (second) and the suffix -ник for day. But Monday is not перник as you would expect (первых + ник), instead Monday is Понедельник. This is short for после (after) не (not) делать (doing) -ник (day), i.e the day after not doing anything (Sunday).
In Finnish a tietosanakirja is an encyclopedia, this is a composed word made from tieto (knowledge) and sanakirja (Dictionary). But also sanakirja is a composed word made out from sana (word) and kirja (book). So an encyclopedia is a book of words of knowledge.
And what makes this even weirder is that in the Roman languages all days are Roman Gods EXCEPT Saturday and Sunday. But there is an explanation for both these things, and it becomes quite clear when you know the days in some Latin language, e.g. in Spanish it’s:
The interesting is the obvious conversion:
Wednesday should have been Hermsday for Hermod who’s the God of messages equivalent to Mercury, but I think they thought it was bad not having a day for the allfather and gave him Wednesday.
What about the weekend? In Spanish (and most other roman languages) they are:
As you can see at some point Latin languages started using their new christian religion to name days, but before that those days were:
So as you can see the days of the week in English are mostly the days of the week from ancient Rome, just adapted to a different culture.
But why didn’t they change Saturday and Sunday? My guess is that because the equivalent of Saturn is Freyr the name would have been too similar to his sister’s day Friday. As for Sunday, in earlier Roman history the Sun wasn’t an important god so Sunday might actually reference the sun and not the deity so no need to convert it. And in later periods the Sun represented Roman imperialism and centralized power so they wouldn’t want that one changed. But these are just guesses from my part, if anyone knows the real reason I would love to hear it.