On a side note, it's not 100% clear (to me, at least) that the word for Monday (ponedelnik) means "per week" or anything about the week per se.
In Russian the word for week is "nedelya", so "ponedelnik" does seem to naturally tie into that. But the word for Sunday in Russian is "voskresenie" (literally means resurrection). Notice this! Every religious word used in non-religious context is suspicious!
If we examine Bulgarian, the week is called "sedmica" (sedm == seven). And Sunday is called "nedelya" (I perceive it as "ne delya" === "no work").
Thus, in Bulgarian the word ponedelnik becomes like "the day after Sunday", rather than "the day starting every week".
Now going back to the Sunday resurrection theme, it's obviously of religious origins, so I dare assume that it may have replaced something that was already there (like nedelya). And then I imagine the people still wanted to keep the word around, so they started using it to mean "week" instead of "Sunday".
If so, then it would make sense that ponedelnik just means "post Sunday".
[The above is just a pet theory I haven't spent any time on, so I'm not guaranteeing its legitimacy]
In Russian the word for week is "nedelya", so "ponedelnik" does seem to naturally tie into that. But the word for Sunday in Russian is "voskresenie" (literally means resurrection). Notice this! Every religious word used in non-religious context is suspicious!
If we examine Bulgarian, the week is called "sedmica" (sedm == seven). And Sunday is called "nedelya" (I perceive it as "ne delya" === "no work").
Thus, in Bulgarian the word ponedelnik becomes like "the day after Sunday", rather than "the day starting every week".
Now going back to the Sunday resurrection theme, it's obviously of religious origins, so I dare assume that it may have replaced something that was already there (like nedelya). And then I imagine the people still wanted to keep the word around, so they started using it to mean "week" instead of "Sunday".
If so, then it would make sense that ponedelnik just means "post Sunday".
[The above is just a pet theory I haven't spent any time on, so I'm not guaranteeing its legitimacy]