oxygen
Pluraloxygens
- 1Molecular oxygen (O₂), a colorless, odorless gas at room temperature made of two bonded oxygen atoms; also called dioxygen.
At room temperature, oxygen exists as a stable two-atom molecule that fuels combustion and respiration.
Plants release oxygen into the atmosphere as a byproduct of photosynthesis.
Note
Everyday talk about oxygen, meaning what we breathe, what fire needs and what plants give off, refers to this two-atom molecule rather than the element itself. Where the difference matters, chemists write O₂ or say dioxygen. Katie L. Burke, writing in American Scientist in 2013, calls what early cyanobacteria released "waste oxygen." The gas began as the leftover of photosynthesis.
- 2A chemical element (symbol O) with atomic number 8 and relative atomic mass 15.9994, occurring as a colorless, odorless gas.
Oxygen ranks as the third most abundant element in the universe by mass.
Nearly half of Earth's crust by weight consists of oxygen bound into minerals.
Note
The name is a learned compound, borrowed into English from French oxygène and built from Greek oxús, "sharp," and génos, "birth" or "kind." The synonym sourstuff renders the same idea in plain native parts, sour standing in for the sharp Greek root. The same origin lies behind every other use of the word, from the breathable gas to the figurative "oxygen of publicity."
- 3A mixture of oxygen and other gases administered to a patient to ease or support breathing.
Paramedics administered oxygen at the scene before moving the accident victim.
After surgery, she was kept on oxygen until her breathing stabilized.
Note
In clinical use the word names a treatment rather than a substance, so it takes the grammar of therapies. A patient is put on oxygen, kept on it or taken off it, and staff give or administer it. The name is shorthand: what the patient breathes is a mixture of gases containing oxygen, not the pure element of the chemistry sense.
- 4A supportive condition or environment that allows something (a movement, an idea, a business) to survive and flourish.
Media coverage provided the oxygen that kept the protest movement alive for months.
Starved of investment, the startup gasped for the oxygen of fresh capital.
Similarlifeblood, fuel, sustenance, nourishment
Note
The metaphor works by withholding as often as by supply: you starve something of oxygen and it dies. Its signature construction is "the oxygen of" plus a noun, as in the oxygen of publicity, or "silence is the oxygen of shame." Adrian Horton, reviewing Mountainhead in 2025, stretches it to a perspective that has claimed far too much oxygen, which is to say too much of the audience's attention.
- 5A single atom of oxygen, the unit that combines with other atoms to form molecules.
Each molecule of water links two hydrogen atoms to a single oxygen.
Carbon dioxide pairs two oxygens with one central carbon atom.
Note
Chemists use this countable shorthand, and it is the reason the plural oxygens exists. Seager and Slabaugh's Chemistry for Today (2013) tells students to look for "a carbon with two oxygens attached" when spotting acetals and ketals. The word counts atoms within a structure, as a carbon does in the same sentence, instead of measuring an amount of gas like the breathable molecule.
Practice
Can you tell the meanings of oxygen apart? Answer 3 quick questions from this page, or write your own sentence and AI will check it.
Origin
Borrowed from French oxygène, a term suggested by Lavoisier for the "acidifying principle," from Ancient Greek ὀξύς (oxús, "sharp") plus γένος (génos, "birth"), reflecting the belief that oxygen played a role in forming acids.