Rheni
Rheni is a Latin form of Rhenus, meaning “the Rhine”. It is the genitive singular masculine noun.
Found 52 times in the Latin texts on Socratos.
Where it is used
Caesar, De Bello Gallico 1.1.6: Belgae ab extremis Galliae finibus oriuntur, pertinent ad inferiorem partem fluminis Rheni, spectant in septentrionem et orientem solem.
All forms of Rhenus (declension table)
Source: Socratos (socratos.org), a free reader for Ancient Greek and Latin. Grammar from the Perseus Treebank and Morpheus; dictionary entries from Lewis & Short, A Latin Dictionary (Perseus Digital Library, CC BY-SA). Counts are from the texts on Socratos.