A root in the Qenya Lexicon of the 1910s given as ᴱ√HEN+U with derivatives having to do with poison (QL/40). Many of the Qenya derivatives begin with f, such as ᴱQ. heno “venom, poison” beside feno and ᴱQ. fent “serpent”, versus ᴱQ. henuva “venomous, poisonous”. Thus I think the true root may have been ᴱ√ǶEN+U or it at least had such a variant, since [[eq|initial and intervocalic ƕ [xʷ] became f]] in Early Qenya. Its Gnomish cognates likewise mostly began with f, such as G. fem “venom” and G. fenog “venomous” (GL/34). There are no signs of this root in Tolkien’s later writing.
Early Primitive Elvish
enu
root. origin‽
enuthi
noun. enuthi
ƕen+u Reconstructed
root. *poison
A root in the Qenya Lexicon of the 1910s glossed “origin” but this gloss was marked with a “?” by Tolkien (QL/35). He did indicate that it was related to ᴱ√ENE whose derivatives had to do with devising and invention, however. In this document, √ENU was the basis for ᴱQ. Enu “God”. Given the later alteration of the Elvish word for God to Q. Eru, it is pretty unlikely the root remained valid in Tolkien’s later conception of the Elvish languages.