# quantum

/ˈkwɑntəm/ (US) · /kwˈɒntəm/ (UK)

Source: https://englishreference.com/word/quantum
Updated: 2026-06-19

## Senses

### 1. physics unit

noun · CEFR C1 · Technical

the smallest possible unit of energy, such as light.

For teachers: the smallest discrete unit of a physical quantity, such as energy or momentum.

- In physics, a photon is a single quantum of light.
- The theory proposes that energy is not continuous but is instead emitted in discrete packets known as quanta.

Usage: The plural form is 'quanta'.

### 2. total amount

noun · CEFR C1 · Formal

a specific amount or the total quantity of something.

For teachers: a required or allowed amount; the total sum or quantity of something.

- The court had to decide the quantum of damages the company should pay.
- The judge spent several hours determining the appropriate quantum of compensation for the claimant's loss of earnings.

Usage: Commonly used in legal contexts regarding money or damages.

### 3. a big change

adjective · CEFR B2

used to describe a change that is very sudden, big, or important.

For teachers: relating to a sudden, significant, or discrete change that moves something to a higher level.

- The new invention was a quantum leap in mobile phone technology.
- The transition from steam power to electricity represented a quantum shift in industrial productivity.

Teaching tip: Often used in the fixed phrase 'quantum leap' or 'quantum shift' to mean a huge improvement.

### 4. quantum physics

adjective · CEFR C1 · Technical

relating to the branch of physics that studies very small particles.

For teachers: pertaining to quantum mechanics or the subatomic properties of matter and energy.

- Scientists are working hard to build the first reliable quantum computer.
- Quantum entanglement remains one of the most counterintuitive phenomena in modern theoretical physics.

## Examples

- A photon is a single quantum of light.
- In physics, energy is not a continuous stream but is instead released in a specific quantum.
- The transition from classical mechanics to a quantum framework required scientists to accept that energy exists in discrete packets rather than as a continuous variable.

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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.