# molecule

/ˈmɑɫəkˌjuɫ/ (US) · /mˈɒlɪkjˌuːl/ (UK)

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

## Senses

### 1. chemical unit

noun · CEFR B2 · Technical

the smallest part of a chemical substance that can exist on its own, made of two or more atoms.

For teachers: the smallest particle of a specific element or compound that retains its chemical properties, consisting of two or more atoms held together by chemical bonds.

- A water molecule is made of two hydrogen atoms and one oxygen atom.
- The researchers used an electron microscope to observe how each individual molecule reacted when exposed to the new catalyst.

Usage: Countable noun in scientific contexts.

### 2. a tiny amount

noun · CEFR C1 · Literary

a very small amount of something.

For teachers: an infinitesimal or extremely small quantity of a substance or quality.

- There was not a single molecule of dust left in the clean room.
- He did not possess a single molecule of common sense, despite his impressive academic credentials.

Teaching tip: This sense is often used in negative sentences to emphasize that something is completely missing.

## Examples

- A water molecule is made of two hydrogen atoms and one oxygen atom.
- When water boils, the heat energy causes the liquid molecules to move faster and spread apart into a gas.
- Researchers engineered a synthetic molecule capable of binding to the virus's surface proteins, effectively neutralizing its ability to infect healthy cells during the initial stages of exposure.

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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.