Some European hydronyms (among them also the river-name Inn) have sometimes been explained based on a root PIE “ *en‑/*on‑” (modern spelling: PIE *h₁en(H)-), which has usually been given the meaning ‘flow, river’ vel sim. This root cannot even be found in Pokorny’s Indogermanisches etymologisches Wörterbuch (1959). No real proof for that root has been found in the appellative lexicon of any Indo-European language. Moreover, there aren’t any sure continuations of that root in the onymic lexicons of those languages. All names put forward as arguments can either be explained based on a root PIE *pen-/*pon- ‘swamp, (standing) water’ (because they are Celtic) or based on a root PIE *h₂en- ‘haul (water)’. As long as no proof of an appellative use of a root PIE *h₁en(H)- can be offered, which alone might tell us, what that root actually meant, the application of ‘Occam’s razor’ leaves us no other choice but to explain all regarding names from the other two roots.