Danube

Attested since at least 1598 (also note Middle English Danby (“Danube”) att. in 15th c. Mandeville's Travels).

Borrowed from Middle French Danube, from Old French Danube, from Latin Dānubius, from Proto-Celtic *Dānowyos (compare Welsh river name Donwy), an extended form of the river-name *Dānu, from Proto-Indo-European *déh₂nu (“river, river goddess”), akin to *dʰenh₂- (“to set in motion; to flow”).

Cognate with Latin fōns (“spring”), Persian دنیدن (danidan, “to hasten, run”), Ossetian дон (don, “water, river”), Sanskrit धन्वति (dhánvati, “it flows, runs”). More at Danube.