# proton

/ˈpɹoʊˌtɑn/ (US) · /pɹˈəʊtɒn/ (UK)

Source: https://englishreference.com/word/proton
Updated: 2026-08-15

## Senses

### 1. subatomic particle

noun · CEFR B2 · Technical

a very small piece of matter inside an atom that has a positive electrical charge.

For teachers: a subatomic particle with a positive charge, found in the nucleus of every atom; the number of protons determines the chemical element.

- Hydrogen is the simplest element because its atom has only one proton.
- The atomic number of an element is defined by the number of protons residing within its nucleus, which remains constant during chemical reactions.

Usage: Countable noun; usually discussed in the context of physics or chemistry.

### 2. biology/embryology

noun · CEFR C2 · Archaic · Technical

an old word for the earliest stage of an organ or tissue in a developing baby or plant.

For teachers: an obsolete synonym for primordium, referring to an organ or part in its most rudimentary form or earliest stage of development.

- In the old textbook, the author used the word proton to describe the start of a leaf.
- Historical anatomical texts occasionally employ the term proton to denote the primitive cellular structures that eventually differentiate into complex organs.

Teaching tip: This sense is obsolete; modern students will only encounter 'proton' in a physics context. Use 'primordium' or 'embryo' for biological contexts instead.

## Examples

- Every atom of hydrogen contains exactly one proton.
- The atomic number of an element is determined by the number of protons found in its nucleus.
- In high-energy physics, researchers use particle accelerators to collide protons at near-light speeds, allowing them to observe the fundamental forces that hold matter together.

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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.