Upon arrival around south Danube and Balkan penninsula, Serbs mixed by domestic population under East Roman Empire. Mostly Celts (or what left from them after centuries of Roman domination) but some other tribes also. So many Serbian words are same as Celtic old one (to name some Chlaan - Clan - Klan..), and so many toponims (mostly) still have the name that was given by Celts (to name some mountan and river Tara, than Baagrdan...).
My real name is really OOld Serbian one, with specific meaning. But it's same case in Romania for example (So we picked up but we also give to some). The same goes for Hungarian language that is full of all kind of Slavic words but Serbs have fair amount of Hungarian in there language, also German, Greeks and Turkish... and lately English.
Religion latter took serious influance on all Sloven's tribes and made them even more different if not by language than by the way of thinking, living (and is still in process as you can see by late "incidents" among sothern tribes).
The biggest Serbian city today is Belgrade (and capitol of mother state - found originally by mentioned Celts tribe SCORODISCS) but also metioned Chicago is in top three Serbian cities in the world - and still growing
).
I'll stop bore you now.
Just as final conclusion, to bad that we don't know for sure who were Slavs, Slovens, Slavens before starting to use that name... old Polish were guesing Saramatian, could be, but hardly!, still we should not moke to this idea cause it still may be true, noone knows much about them eather.
Regards to all you and please forgive my typos and some likely grammars errors.
And once more
Tathy CHEERS