A noun meaning “river” developed from the primitive form ᴹ✶kelun (Ety/KEL), where the [[ilk|final [un] became [on]]].
Conceptual Development: This word was initially marked as Noldorin.
Doriathrin
duil
noun. river
celon
noun. river
There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
A noun meaning “river”, simply an elaboration of its root ᴹ√DUY (Ety/DUI).