Definition of oxygen
1
: a chemical element that constitutes 21 percent of the Earth's atmosphere, that is capable of combining with all elements except some noble gases, that is active in physiological processes of almost all known organisms, and that is involved especially in combustion — see Chemical Elements Table
2
: something that sustains or fuels
disagreement is the true oxygen of these magazines— Joseph Epstein
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Merriam-Webster unabridged
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Time Traveler for oxygen
The first known use of oxygen was in 1788
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