As a political compromise, the Constitution of Yugoslavia was amended in 1968 to introduce "Muslims" in a national (as opposed to religious) sense; effectively recognizing a constitutive nation whilst avoiding the recognition of "Bosniak" or "Bosnian" as ethnic or national designations.
the suffix -(n)in had been replaced by -ak to create the current form Bošnjak (Bosniak), first attested in the diplomacy of Bosnian king Tvrtko II who in 1440 dispatched a delegation (Apparatu virisque insignis) to the Polish king of Hungary, Władysław Warneńczyk (1440–1444), asserting a common Slavic ancestry and language between the Bosniak and Pole.
The Miroslav Krleža Lexicographical Institute thus defines Bosniak as "the name for the subjects of the Bosnian rulers in the pre-Ottoman era, subjects of the Sultans during the Ottoman era, and the current name for the most numerous of the three constituent peoples in Bosnia and Herzegovina.
However, the concept of nationhood was foreign to the Ottomans at that time – not to mention the idea that Muslims and Christians of some military province could foster any common supra-confessional sense of identity.
The inhabitants of Bosnia called themselves various names: from Bosniak, in the full spectrum of the word's meaning with a foundation as a territorial designation, through a series of regional and confessional names, all the way to modern-day national ones.
According to philologist Anton Mayer the name Bosna could essentially be derived from Illyrian Bass-an-as(-ā) which would be a diversion of the Proto-Indo-European root *bhoĝ-, meaning "the running water".