n.
 the chemical element of atomic number 8, a colourless, odourless reactive gas that forms about 20 per cent of the earth's atmosphere and is essential to plant and animal life. 
(Symbol: 
O)
 
  Derivative
  
    - oxygenic adj.
  - oxygenous adj.
 
   
  Etymology
  C18: from Fr. (principe) oxygène ‘acidifying constituent’ (because at first it was held to be the essential component of acids).