Bosnia (region)
Bosnia (/Босна; ) is the northern region of Bosnia and Herzegovina, encompassing roughly 81% of the country; the other eponymous region, the southern part, is Herzegovina. "Bosnia" is an informal term for the whole country.
Bosniaks
The Bosniaks derive their ethnonym from Bosnia, first mentioned in "De Administrando Imperio" by the Byzantine emperor Constantine VII as the "horion" ("small country") of "Bosona" (Βοσωνα). Linguists have traditionally proposed the name to be derived from the eponymous river "Bosna"; believed to be a pre-Slavic hydronym in origin and possibly mentioned for the first time during the 1st century AD by Roman historian Marcus Velleius Paterculus under the name "Bathinus flumen". Another basic source associated with the hydronym "Bathinus" is the Salonitan inscription of the governor of Dalmatia, Publius Cornelius Dolabella, where it is stated that the "Bathinum" river divides the Breuci from the Osseriates.
Some scholars also connect the Roman road station "Ad Basante", first attested in the 5th century "Tabula Peutingeriana", to Bosnia. According to the English medievalist William Miller in the work "Essays on the Latin Orient" (1921), the Slavic settlers in Bosnia "adapted the Latin designation [...] Basante, to their own idiom by calling the stream Bosna and themselves Bosniaks [...]".
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". The Croatian linguist, and one of the world's foremost onomastics experts, Petar Skok expressed an opinion that the chronological transformation of this hydronym from the Roman times to its final Slavicization occurred in the following order; *"Bassanus"> *"Bassenus"> *"Bassinus"> *"Bosina"> "Bosьna"> "Bosna".
Other theories involve the rare Latin term "Bosina", meaning boundary, and possible Slavic and Thracian origins. Theories that advocates the link of the name Bosnia, and thus of the Bosniaks with the Early Slavs of northern Europe has initially been proposed by the 19th century historians Joachim Lelewel and Johann Kaspar Zeuss, who considered the name of Bosnia to be derived from a Slavic ethnonym, Buzhans (Latin: "Busani"), mentioned in the Primary Chronicle and by the Geographus Bavarus in his "Description of cities and lands north of the Danube". According to both Lelewel and Zeuss Buzhans settled in Bosnia. The theory of Slavic origin of the name Bosnia and it's possible connection with the Slavic tribe of Buzhans, came also to be advocated by the 20th and 21th century Yugoslav and Bosnian historians such as Marko Vego, Muhamed Hadžijahić and Mustafa Imamović. 
For the duration of Ottoman rule, the word Bosniak came to refer to all inhabitants of Bosnia; Turkish terms such as ""Boşnak milleti"", ""Boşnak kavmi"", and ""Boşnak taifesi"" (all meaning, roughly, "the Bosnian people"), were used in the Empire to describe Bosnians in an ethnic or "tribal" sense; and indeed, 17th-century Ottoman traveler and writer Evliya Çelebi reports in his work "Seyahatname" of the people in Bosnia as natively known as Bosniaks (Bošnjaci). 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. In this regard, Christian Bosnians had not described themselves as either Serbs or Croats prior to the 19th century, and in particular before the Austrian occupation in 1878, when the current tri-ethnic reality of Bosnia and Herzegovina was configured based on religious affiliation. Social anthropologist Tone Bringa develops that "Neither Bosniak, nor Croat, nor Serb identities can be fully understood with reference only to Islam or Christianity respectively, but have to be considered in a specific Bosnian context that has resulted in a shared history and locality among Bosnians of Islamic as well as Christian backgrounds."