Why недеља means both Sunday and week
Serbian's word for Sunday, недеља, is also its word for an entire week - and once you know why, the other six day names stop looking arbitrary. Four of them turn out to be nothing but numbers, and even Russian's own понедельник is still quietly built on the very meaning Russian itself stopped using centuries ago.
This platform's own lesson on days and months mentions it almost in passing: недеља means both Sunday and week, and context is left to sort out which. That is a strange thing for a language to do - imagine English using Sunday to also mean week - and it turns out to be the loose end of a much bigger story: nearly every day name in Serbian is either a leftover number or a fossil of exactly this ambiguity.
A day named not working
Недеља comes from a Common Slavic compound of не (not) and an old verb related to делати (to do, to work): literally, the day of not working. In the earliest Slavic usage this named one specific day - the day of rest - not a span of seven. Serbian never gave that meaning up, and it is not alone: Polish niedziela, Czech neděle and Bulgarian неделя all still mean Sunday today, not week. Once you line those up, Serbian is not the language behaving oddly here.
Russia's other Sunday
Russian is the outlier, and church history explains why. As Orthodox Christianity took hold, Church usage wanted Sunday named for what it actually commemorates - the Resurrection - and Russian settled on воскресенье, built on воскресение (resurrection), for the day itself. That freed неделя to drift: with no fixed day to anchor to anymore, it slid toward naming the whole stretch of days built around it, which is the only meaning it carries in Russian today. Serbian's church took the same theology without making the same lexical swap - недеља kept naming the day, and only secondarily came to also label the week around it.
Here is the irony: Russian's own word for Monday, понедельник, is built the same way as Serbian's понедељак - the day after недеља. Russian kept that compound without noticing, or minding, that its own неделя no longer means the day the compound refers to. Say понедельник in Russian and you are still, quietly, saying the day after Sunday in a language where Sunday is a different word entirely.
The rest of the week is just arithmetic
Once недеља anchors the week as day one, four of the remaining five weekday names in Serbian turn out to be nothing more than old ordinal numbers, counted outward from it.
| Weekday | Built from |
|---|---|
| ponedeljak | po + nedelja |
| utorak | drugi |
| sreda | sredina |
| četvrtak | četvrti |
| petak | peti |
Понедељак is the day after недеља, spelled out. Уторак is built on an old word for second, the same root visible in modern Serbian's ordinal други. Среда is literally the middle - the midpoint of the working week. Четвртак and петак are fourth and fifth with no disguise at all. Only субота breaks the pattern: it is a loanword, reaching Serbian through Church Slavonic from Hebrew Shabbat, the same origin as the English Saturday shares indirectly through Latin Sabbatum - a borrowed name for a borrowed day of rest, sitting one day before the native Slavic one.
If the double meaning of недеља ever genuinely confuses a sentence, Serbian has an escape hatch: седмица names the seven-day span and nothing else, unambiguous at the cost of sounding slightly more formal than everyday недеља.
Ne radim nedeljom.
I don't work on Sundays.
Here недељом can only mean the day - the sentence names a weekly habit tied to one specific day, not a stretch of time.
Vraćam se za nedelju dana.
I'll be back in a week.
Adding дана (of days) is what tips this reading toward the span rather than the day - a common disambiguating chunk.