Slověn / Slovan (in a so-called non-productive form) would have been an appellative similar to bratěn / bratan which de facto confirms a thesis of the Slavs as those «linguistically» related. Among the Slavists, it was by no means less popular searching for a word base in a word sláva (glory) as an Adam Czarnocki’s quotation attests.
Source: wiktionary