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)  
<noun.substance>
<noun.substance>
| Se |   | 
| atomic number 34 |   | 
| selenium |   | 
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substance holonym
