Selenium

n. nonmetallic chemical element (Chemistry)

Selenium (IPA: ) is a chemical element with atomic number 34, with the chemical symbol Se. It is a nonmetal, chemically related to sulfur and tellurium, and rarely occurring in its elemental state in nature. It is toxic in large amounts, but trace amounts of it are necessary for cellular function in most, if not all, animals, forming the active center of certain enzymes. Selenium is an essential component of the enzyme glutathione peroxidase (GSH-Px) which catalyzes the reaction:2 GSH+ H2O2---------GSH-Px → GSSG + 2 H2O
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Selenium /se·le·ni·um/ a chemical element, at. no. 34, symbol Se; it is an essential mineral nutrient, being a constituent of the enzyme glutathione [more]Selenium - Community and Resources

Noun
1. a toxic nonmetallic element related to sulfur and tellurium; occurs in several allotropic forms; a stable gray metallike allotrope conducts electricity better in the light than in the dark and is used in photocells; occurs in sulfide ores (as pyrite)
(synonym) Se, atomic number 34
(hypernym) chemical element, element
(substance-holonym) pyrite, iron pyrite, fool's gold

n. selenium, nonmetallic chemical element (Chemistry)