English Reference
noun

oxygen

n.
US /ˈɑksədʒən/ UK /ˈɒksɪdʒən/ oxy·gen UK spelling oxygens

  1. 01 B1 Intermediate Science

    the gas in the air that you need to breathe to stay alive.

    the molecular form of the element (O₂) which constitutes approximately 21 percent of the Earth's atmosphere and is vital for life.

    Simple

    The doctor gave the patient some oxygen to help him breathe more easily.

    In context

    Plants produce oxygen during photosynthesis, which is then released into the atmosphere and used by animals for cellular respiration.

    Usage

    Uncountable when referring to the gas in general; countable only in technical chemical contexts referring to specific atoms.

  2. 02 B2 Upper Intermediate Technical Science

    the chemical element with the symbol O and atomic number 8.

    the chemical element with atomic number 8; it is the most abundant element by mass in the Earth's crust.

    Simple

    Water is made of two parts hydrogen and one part oxygen.

    In context

    The researcher analyzed the isotopes of oxygen found within the ice core samples to determine historical temperature fluctuations.

  3. 03 C1 Advanced Literary

    the things or attention that an idea or project needs to grow and succeed.

    the metaphorical 'air' or support required for an idea, movement, or person to flourish or remain relevant.

    Simple

    The new law gave the small business community the oxygen it needed to grow.

    In context

    By refusing to debate the extremist group, the prime minister denied them the oxygen of publicity they so desperately craved.

Usage oxygen levels

A key feature of this period was that oxygen levels were much lower than they are today.

Phys.org· 2 Sept 2026

The body responds by sending more blood toward the skin to release that heat while continuing to supply oxygen to working muscles.

The Conversation· 27 Aug 2026

Etymology tree Proto-Indo-European *h₂eḱ-der.? Ancient Greek ὀξύς (oxús) Proto-Indo-European *ǵenh₁- Proto-Indo-European *-os Proto-Indo-European *ǵénh₁os Proto-Hellenic *génos Ancient Greek γένος (génos) French oxygènebor. English oxygen 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. By surface analysis, oxy- + -gen.

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

This entry
Origin Ancient Greek ὀξύς
Level B2 · Upper Intermediate
Frequency Common
Updated