There are several supposed etymologies of the name "Papuk", it's almost certainly not of Croatian origin. One is that it comes by assimilation from earlier "Bapuk", where "Ba" is the name of the Celtic tribe that inhabited the region, and "Puk" comes from the Indo-European root *peiH, meaning "big". However, from the historical sources, it's visible that Papuk was originally a hydronym.[4] Based on that, it's been suggested that the name comes from the repetitive of the Indo-European root *bhogj (to flow), *bhebhogj, so that it means "that which flows and flows".