A word appearing in Quenya Notes (QN) from 1957 glossed “(a) poison(ous substance)” and derived from √SLOY (PE17/185).
Conceptual Development: The Qenya Lexicon of the 1910s had ᴱQ. heno (henu-) “venom, poison” under the early root ᴱ√HEN+U (QL/40), with a variant feno (QL/38). The contemporaneous Poetic and Mythological Words of Eldarissa had only the stem form henŭ- “venom” (PME/40). In The Etymologies of the 1930s Tolkien had a completely different word ᴹQ. sangwa “poison” derived from primitive ᴹ✶sagmā under the root ᴹ√SAG (Ety/SAG).
Neo-Quenya: For purposes of Neo-Quenya, I would stick to the 1957 word hloima, used for a specific poison or poisonous substance, as opposed to hloirë for poisonousness or poison in the abstract.
hloima noun "poison", "a poisonous substance" (PE17:185)