arsenic
n. uncountablen. a chemical element that is famous for being a very strong poison. It is a greyish-silver metal that can be found in nature.
n. a brittle, steel-grey metalloid element that is highly toxic in its inorganic forms. Often associated with historical toxicology and industrial processes.
The old pipes were tested for traces of arsenic.
Environmental scientists monitored the groundwater near the old mine to ensure arsenic levels remained within safe limits.
While arsenic is notoriously known as a potent poison in literature, it also has legitimate industrial applications in the strengthening of copper and lead alloys.
From Middle English arsenik, borrowed from Middle French arsenic, from Latin arsenicum, from Ancient Greek ἀρσενικόν (arsenikón, “yellow arsenic”) (influenced by ἀρσενικός (arsenikós, “potent, virile”)), from Semitic (compare Classical Syriac ܙܪܢܝܟܐ (zarnīḵā), Aramaic 𐡆𐡓𐡍𐡉𐡊𐡀 (zrnykʾ /zarnīḵā/)), from Middle Iranian zarnīk (compare Persian زرنیخ (zirnīx /zernix, zarnīx /zarnix, “arsenic”), زرنی (zurnī /zorni), Bakhtiari زرنیق (zarniq)), from Old Median zaraniyakā (compare Avestan 𐬰𐬀𐬭𐬀𐬥𐬌𐬌𐬀 (zaraniia, “golden”), Old Persian 𐎭𐎼𐎴𐎡𐎹 (d-r-n-i-y /daraniya-/, “gold”), Sanskrit हिरण्य (híraṇya, “gold”), Persian زر (zar, “gold”)), ultimately from Proto-Indo-European *ǵʰelh₃-. More at yellow.
Uncountable when referring to the chemical element or the poison; can be countable in a chemistry context when referring to specific compounds.