This noun appeared as ingwil or ingwilin (ingwiling-) “eel” in the Qenya Lexicon of the 1910s, a combination of ᴱQ. ingwe “fish” and ᴱQ. lin (ling-) “snake” (QL/43). The word ingwil(in) “eel” also appeared in the Poetic and Mythological Words of Eldarissa (PME/43).

Neo-Quenya: I would update this word to ᴺQ. lingwileuca “eel” for purposes of Neo-Quenya, a combination of the later words Q. lingwë “fish” and Q. leuca “snake”.