Beware, older languages below! The languages below were invented during Tolkien's earlier period and should be used with caution. Remember to never, ever mix words from different languages!

Qenya 

kelut

noun. rivulet

A noun for “rivulet” in the Declension of Nouns of the early 1930s (PE21/33, 35), clearly a derivative of ᴹ√KEL(U) “flow”.

Qenya [PE21/33; PE21/35] Group: Eldamo. Published by

nelle

noun. brook, brook, *stream

A noun in The Etymologies of the 1930s glossed “brook” derived from primitive ᴹ✶nenle (Ety/NEN), where the ancient nl became ll (PE19/47).

siril

noun. rivulet

A noun for “rivulet” in The Etymologies of the 1930s derived from the root ᴹ√SIR “flow” (Ety/SIR).