selenium Meaning, Definition & Usage

  1. noun a toxic nonmetallic element related to sulfur and tellurium; occurs in several allotropic forms; a stable grey metallike allotrope conducts electricity better in the light than in the dark and is used in photocells; occurs in sulfide ores (as pyrite)
    atomic number 34; Se.

WordNet

Se*le"ni*um noun
Etymology
NL., from Gr. the moon. So called because of its chemical analogy to tellurium (from L. tellus the earth), being, as it were, a companion to it.
Definitions
  1. (Chem.) A nonmetallic element of the sulphur group, and analogous to sulphur in its compounds. It is found in small quantities with sulphur and some sulphur ores, and obtained in the free state as a dark reddish powder or crystalline mass, or as a dark metallic-looking substance. It exhibits under the action of light a remarkable variation in electric conductivity, and is used in certain electric apparatus. Symbol Se. Atomic weight 78.9.

Webster 1913