ENGLISH
REFERENCE

quantum

n. · adj.
US //ˈkwɑntəm// UK //kwˈɒntəm// quan·tum
  1. 1 physics unit (n.)
    C1 Advanced Technical Science

    the smallest possible unit of energy, such as light.

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

    Example

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

    Example

    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. 2 total amount (n.)
    C1 Advanced Formal

    a specific amount or the total quantity of something.

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

    Example

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

    Example

    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.

Show 2 more sensesShow fewer
  1. 3 a big change (adj.)
    B2 Upper Intermediate

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

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

    Example

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

    Example

    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.

  2. 4 quantum physics (adj.)
    C1 Advanced Technical Science

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

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

    Example

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

    Example

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

Origin

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

Idioms1 entry

© 2026 English Reference