Medieval Hum (Herzegovina) was a different kingdom from kingdom of Bosnia, it existed separately and had it's own rulers until coming under rule of Bosnian king Tvrtko I Kotromanić. Later Hum nobles reclaimed their independence, yet eventually getting conquered by Ottomans in middle of 15th century. So, Bosnia was a name of different kingdom that didn't enclude Hum at it's formation.

Herzegovina also means ''dukedom'', as herceg is a duke in medieval Serbian. But Bosnia geographicaly includes only a region around Sarajevo and current central Bosnia, to the west land is geographicaly known as Krajina, to the north Posavina, to the northeast Semberija, to the east Podrinje. It could have all entered in a name of a state, yet Herzegovina managed in the end probably because of its medieval history.