oxygen

Etymology

Borrowed from French oxygène (originally in the form principe oxygène, a variant of principe oxigine ‘acidifying principle’, suggested by Lavoisier), from Ancient Greek ὀξύς (oxús, “sharp”) + γένος (génos, “birth”), referring to oxygen's supposed role in the formation of acids.

noun

1. The chemical element (symbol O) with an atomic number of 8 and relative atomic mass of 15.9994. It is a colorless and odorless gas.
2. Molecular oxygen (O₂), a colorless, odorless gas at room temperature, also called dioxygen.
   Oxygen levels on Earth skyrocketed 2.4 billion years ago, when cyanobacteria evolved photosynthesis: the ability to convert water and carbon dioxide into carbohydrates and waste oxygen using solar energy. The evolutionary precursor of photosynthesis is still under debate, and a new study sheds light. 2013 September-October, Katie L. Burke, “In the News”, in American Scientist
3. (medicine) A mixture of oxygen and other gases, administered to a patient to help them breathe.
4. (countable) An atom of this element.
   Look first at any structure to see if there is a carbon with two oxygens attached. Hemiacetals, hemiketals, acetals, and ketals are all alike in that regard. 2013, Spencer L. Seager, Michael R. Slabaugh, Chemistry for Today: General, Organic, and Biochemistry, page 479
5. (figurative) A condition or environment in which something can thrive.
   Silence is the oxygen of shame.
   They hoped to starve the terrorists of the oxygen of publicity.