# hydrogen

/ˈhaɪdɹədʒən/ (US) · /hˈaɪdɹədʒən/ (UK)

Source: https://englishreference.com/word/hydrogen
Updated: 2026-06-20

## Senses

### 1. chemical element

noun · CEFR B1 · Technical

the simplest and lightest chemical element, found in water and all living things.

For teachers: the chemical element with atomic number 1 and symbol H. Uncountable when referring to the element in a general or chemical sense.

- Hydrogen is the most common element in the entire universe.
- Hydrogen atoms consist of a single proton and a single electron, making it the simplest and most abundant element in the cosmos.

Usage: Often used as a modifier in compound nouns like 'hydrogen atom' or 'hydrogen bond'.

### 2. flammable gas

noun · CEFR B2 · Technical

a gas with no colour or smell that burns very easily and can be used as fuel.

For teachers: molecular hydrogen (H₂) existing as a colourless, odourless, and highly flammable gas at standard temperature and pressure.

- The car runs on hydrogen instead of petrol to help the environment.
- The experimental aircraft was powered by liquid hydrogen, which requires specialised storage tanks to maintain extremely low temperatures.

Usage: Commonly used with verbs like 'burn', 'store', or 'produce'.

## Examples

- Hydrogen is the main fuel for the sun.
- Scientists are researching how to use hydrogen as a clean fuel source for cars and buses.
- The fusion of hydrogen nuclei into helium within the core of a star releases the immense energy that sustains its luminosity over billions of years.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.