Wow! Wiktionary suggests that the Franks (from whom these derive) themselves were named after a word for "spear".
An amazing one that I've found striking for a while and that also involves an ethnic group is
ciao - slave - Slav
> Borrowed from Italian ciao (“hello, goodbye”), from Venetian ciao (“hello, goodbye, your (humble) servant”), from Venetian s-ciao / s-ciavo (“servant, slave”), from Medieval Latin sclavus (“Slav, slave”), related also to Italian schiavo, English Slav, slave and Old Venetian S-ciavón ("Slav"), from Latin Sclavonia (“Slavonia”).
The etymology of the Slavs' autonym itself is much more disputed, but possibly derives from the Slavic word for "word", so meaning "people who can talk", among several totally different suggestions. https://en.wiktionary.org/wiki/Reconstruction:Proto-Slavic/s...
> The etymology of the Slavs' autonym itself is much more disputed, but possibly derives from the Slavic word for "word", so meaning "people who can talk", among several totally different suggestions.
Well in pretty much every Slavic language analog of "słowo" is "word" and "słowianin" is Slav. And in most of these languages the word for Germans (the most common non-Slavic foreigners) is analog of "Niemiec" which is the same word root as "mute person" (niemy).
The Wiktionary quick summary of why it's disputed is one researcher's assertion that "slověne can't be formed from slovo because -ěninъ, -aninъ only occurs in derivations from place names". (Maybe słowianin < slověninъ is an exception, but you can see where someone might be skeptical if it's supposedly the only* exception!)
Sometimes etymologies that feel super-logical turn out to be more complicated historically. In many of these cases, the later perception that two words were related influenced their subsequent meaning or spelling, even if they were originally not related.
As a non-speaker of Slavic languages, I'm pretty convinced about the "word" connection, especially with the example you mentioned about the Germans being called "non-talkers", since it's not very unusual for ethnic groups' autonyms to mean something like "speakers". But there are lots of etymologies that feel natural and straightforward and are later shown to have a folk etymological component.
Indeed I can't find in Polish any other singular -anin not derived from place, But słowianin in plural is słowianie, and there's lots of -anie words not derived from places.
For example abstract nouns formed from verbs, like:
pisanie (writing) from pisać (to write)
palenie (smoking) from palić (to burn)
śniadanie (breakfast) from archaic śniadać (to eat)
jedzenie (food) from modern jeść (to eat)
bieganie (running) from biec (to run)
etc. There's easily hundreds of these.
Then it would be
słowianie (abstract noun for people who can talk) from archaic słowić (to express in words)
The only weird thing would be that słowianie is plural and all of the other -anie nouns made from verbs are singular.
From which we get Wales, Cornwall, Gaul, Walloon, and Wallachia. Originally the name of a particular tribe, but came to refer to angry foreign neighbours more generally.
An amazing one that I've found striking for a while and that also involves an ethnic group is
ciao - slave - Slav
> Borrowed from Italian ciao (“hello, goodbye”), from Venetian ciao (“hello, goodbye, your (humble) servant”), from Venetian s-ciao / s-ciavo (“servant, slave”), from Medieval Latin sclavus (“Slav, slave”), related also to Italian schiavo, English Slav, slave and Old Venetian S-ciavón ("Slav"), from Latin Sclavonia (“Slavonia”).
https://en.wiktionary.org/wiki/ciao#Etymology
https://en.wiktionary.org/wiki/slave#English "because Slavs were often forced into slavery in the Middle Ages"
The etymology of the Slavs' autonym itself is much more disputed, but possibly derives from the Slavic word for "word", so meaning "people who can talk", among several totally different suggestions. https://en.wiktionary.org/wiki/Reconstruction:Proto-Slavic/s...