English Reference
noun · adjective

quantum

n. · adj.
US /ˈkwɑntəm/ UK /kwˈɒntəm/ quan·tum

  1. 01 C1 Advanced Technical Science

    n.the smallest possible unit of energy, such as light.

    n.the smallest discrete unit of a physical quantity, such as energy or momentum.

    Simple

    In physics, a photon is a single quantum of light.

    In context

    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. 02 C1 Advanced Formal

    n.a specific amount or the total quantity of something.

    n.a required or allowed amount; the total sum or quantity of something.

    Simple

    The court had to decide the quantum of damages the company should pay.

    In context

    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. 03 B2 Upper Intermediate

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

    adj.relating to a sudden, significant, or discrete change that moves something to a higher level.

    Simple

    The new invention was a quantum leap in mobile phone technology.

    In context

    The transition from steam power to electricity represented a quantum shift in industrial productivity.

    Teacher's tip

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

  4. 04 C1 Advanced Technical Science

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

    adj.pertaining to quantum mechanics or the subatomic properties of matter and energy.

    Simple

    Scientists are working hard to build the first reliable quantum computer.

    In context

    Quantum entanglement remains one of the most counterintuitive phenomena in modern theoretical physics.

Usage quantum computing · quantum systems · quantum computer

His research is the bluest of blue-sky: he uses quantum computers to predict how sub-atomic particles behave.

BBC News· 18 Mar 2026

Physicists have found a new way to peer inside one of matter’s most elusive quantum states: the Wigner crystal, where electrons stop behaving like independent particles and organize into a crystal-like pattern.

ScienceDaily· 12 Aug 2026

From Late Latin quantum, noun use of neuter form of Latin quantus (“how much”).

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

This entry
Origin Latin quantus
Level C2 · Proficiency
Frequency Common
Updated