Oxygen

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.
3. A mixture of oxygen and other gases, administered to a patient to help them breathe.
4. An atom of this element.