A word appearing in Quenya Notes (QN) from 1957 derived from √SLOY, the equivalent of Q. hloirë “venom, poison(ousness)” (PE17/185).
Conceptual Development: In the Gnomish Lexicon of the 1910s Tolkien had G. fem “venom (of snakes), poison in general” (GL/34), likely the equivalent of ᴱQ. heno “venom, poison” based on the early root ᴱ√HEN+U (QL/40).
Neo-Sindarin: For purposes of Neo-Sindarin, I would stick to the 1957 word lhoer used for poison in general or in the abstract, as opposed to a specific poison or poisonous substance which would be lhoew.
n. venom, poison(ousness). Q. hloire.