Eureka (word)
The exclamation 'Eureka!' is attributed to the ancient Greek scholar Archimedes. He reportedly proclaimed "Eureka! Eureka!" after he had stepped into a bath and noticed that the water level rose, whereupon he suddenly understood that the volume of water displaced must be equal to the volume of the part of his body he had submerged. (This relation is "not" what is known as Archimedes' principle—that deals with the "upthrust" experienced by a body immersed in a fluid.) He then realized that the volume of irregular objects could be measured with precision, a previously intractable problem. He is said to have been so eager to share his discovery that he leapt out of his bathtub and ran naked through the streets of Syracuse.
Papuk
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. 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". However, there are several problems with that etymology. First, it's visible by hydronyms such as "Bosut" and "Bosna" that Indo-European *bh gave *b in the local language. Second, *bhebhogj would actually mean "flow and flow" and not "that which flows and flows", so the endings don't match. So, it's been suggested that the name is of Pre-Indo-European origin.