selenium

American  

[si-lee-nee-uhm] / sɪˈli ni əm /

noun

Chemistry.

1. a nonmetallic element chemically resembling sulfur and tellurium, occurring in several allotropic forms, as crystalline and amorphous, and having an electrical resistance that varies under the influence of light. Se; 78.96; 34; (gray) 4.80 at 25°C, (red) 4.50 at 25°C.

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selenium British  

/ sɪˈliːnɪəm /

noun

1. a nonmetallic element that exists in several allotropic forms. It occurs free in volcanic areas and in sulphide ores, esp pyrite. The common form is a grey crystalline solid that is photoconductive, photovoltaic, and semiconducting: used in photocells, solar cells, and in xerography. Symbol: Se; atomic no: 34; atomic wt: 78.96; valency: –2, 4, or 6; relative density: 4.79 (grey); melting pt: 221°C (grey); boiling pt: 685°C (grey)

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selenium Scientific  

/ sĭ-lē′nē-əm /

1. A nonmetallic element that occurs in a gray crystalline form, as a red powder, or as a black glassy material. It is highly photosensitive and can be used to convert light into electricity. Its ability to conduct electricity also increases with higher exposure to light. For these reasons selenium is used in photocopying technology, photography, and solar cells. Atomic number 34; atomic weight 78.96; melting point 217°C; boiling point 684.9°C; specific gravity (gray) 4.79; (red) 4.5; (black) 4.28; valence 2, 4, or 6.

2. See Periodic Table

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Etymology

Origin of selenium

< New Latin (1818) < Greek selḗn ( ē ) moon + New Latin -ium -ium; named in allusion to its similarity to tellurium

Example Sentences

Selenium can be found in products such as electronics, glass, plastics, pesticides, shampoos and rubber.

From Los Angeles Times • May 4, 2025

Selenium itself is an oxidant, but in low doses it activates responses in a controlled manner, predisposing the body to better defense.

From Science Daily • Oct. 30, 2023

Selenium is an essential nutrient that lowers the risk of developing cancer.

From Salon • Sep. 7, 2023

Selenium has always been wellknown for its anti-inflammatory effects, but CoQ10 was rather surprising here: http://www.q10facts.com/coenzyme-q10-and-inflammation/

From New York Times • Jan. 18, 2018

Selenium gives off the smell of decayed horse-radish.

From A System of Instruction in the Practical Use of the Blowpipe Being A Graduated Course Of Analysis For The Use Of Students And All Those Engaged In The Examination Of Metallic Combinations by Anonymous