From a Gaulish *Rēnos (which was also the source of Proto-Germanic *Rīnaz). The Greek form is recorded in Strabo’s Geographica (1.4.3), written between 20 BC and AD 20, slightly later than the Latin equivalent Rhenus (Cicerio, In Pisonem, ca. 55 BC).
The Gaulish name is from the Proto-Indo-European root *rey- (“to flow”).
- the river Rhine
- Woodhouse, S. C. (1910) English-Greek Dictionary: A Vocabulary of the Attic Language, London: Routledge & Kegan Paul Limited, page 1,024