oxygen

noun

1. (countable, uncountable)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. Sometimes called elemental oxygen to distinguish it from molecular oxygen.

   “Holonyms: dioxygen, O₂, oxygen (loose sense)”

   “By molar fraction, calcium oxide contains equal parts calcium and oxygen.”

2. (countable, uncountable)Molecular oxygen (O₂), a colorless, odorless gas at room temperature.

   “Meronym: oxygen (strict sense)”

   “About 21% of the air you breathe is oxygen.”

   “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.”

3. (countable, uncountable)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.”

5. (countable, figuratively, uncountable)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.”

   “. I found myself longing for more than two minutes with the girlfriend, the ex-wife, the assistant, the board member, let alone one of the many staff at the house – anyone to de-center a perspective that has already claimed far too much oxygen in the public sphere.”