Now this is slightly confusing: I know the word smut from Lower German dialects, as a noun of the related word smutsig (and the High German cognates, schmutzig and Schmutz), but funnily, the Poles picked the word to describe it as sad, i.e. feeling sad. The apparent noun is smutny. I will just assume that the noun to the Swedish adjective is smuts, to show its relation with the German language. It just is an interesting path to draw relations between dirt and a depressive mood, it shows some deep understanding of atmosphere and feelings, that preceded the creation of the apparent nouns and adjectives.
smutny is from old slavic. in serbian we have mutno (blurry), mutiti (to mix), smutno vreme (troubled time), mut seems to mean mixed, tumbled, while s prefix adds the finished aspect. it is not borrowed from german word for dirty. but there could be an older Indo-European connection. I can't verify this since I don't have access to an etymological dictionary though.
My PIE dictionary lists the root meut- as the word from which the Polish smutny derived, but couldn't find the other terms you mentioned as related to the word smutny.
Still, at least I could find the root for smutny, which also brought up the word *smuð-lṓn, which is likely... Yes, what is it? I cannot guess the Proto-language, but it also introduced the root for Lithuanian “smũtnas”.
Anyway, thanks a lot for your clarification!
I'm not surprised you can't find them, those words are contemporary, not ancient. I mentioned them because they are naturally derived from a slavic root, not borrowed (muti, mutiti, zamutiti, zamućeno, mutno, smutno...). If you don't mind me asking, what PIE dictionary are you using?
Wouldn't this actually be a reason why I should be able to find them? Of course one does not spontaneously start compiling an etymological dictionary of the PIE language and which words of multiple European languages derived from words in this language, so that modern-day words that emerged only recently were not added yet—it would likely suffice to create a dictionary in a national language which then included such words with their apparent derivates—, but still I would expect such regular ones to be added. Alas, who am I to blame anyone?
The one by Julius Pokorny, an edition from 2007. I found it online, for free, as a PDF. It may not be the best by linguists' standards, but for quick searches, and for private usage, I find it highly valuable.
You're welcome! I hope it suits your expectations. I for myself have no knowledge of PIE linguistics or how to detect good investigations into the roots of lexical words in European languages, so that I cannot warrant for its quality. A professional linguist might be abler to recommend another worthwhile etymological dictionary, just in case you are disappointed by my recommendation.
Have a nice day!