Definition of quantum in English:

Share this entry


Pronunciation: /ˈkwɒntəm/

noun (plural quanta /ˈkwɒntə/)

1 Physics A discrete quantity of energy proportional in magnitude to the frequency of the radiation it represents.
Example sentences
  • This excess energy is emitted in quanta of electromagnetic radiation (photons of light) that have exactly same energy as the difference in energy between the orbits jumped by the electron.
  • Bohr realized that the idea of a quantum of energy could explain how the electrons in the atom are arranged.
  • To drop from a higher to a lower, it emitted a quantum of energy.
1.1An analogous discrete amount of any other physical quantity, such as momentum or electric charge.
Example sentences
  • Light bullets are the quanta of the electromagnetic field and are known as photons.
  • A second problem also led to a quantum theory of light, and this time to a belief in the physical reality of the quanta.
  • These symmetries tie together particles usually considered constituents of matter (like quarks and electrons) with the quanta of forces (like photons and gluons).
1.2 Physiology The unit quantity of acetylcholine released at a neuromuscular junction by a single synaptic vesicle, contributing a discrete small voltage to the measured end-plate potential.
Example sentences
  • Responses ensuing from the spontaneous release of single quanta are termed miniature excitatory junctional currents (mEJCs).
  • In the crayfish leg extensor preparation, the number of quanta released per action potential (quantal content) was approximately 15, at low frequencies of stimulation.
  • What fraction of receptors are saturated following the release of a single quantum, and is a larger synapse, with more receptors less saturated than a smaller one?
2A required or allowed amount, especially an amount of money legally payable in damages: the court must determine the quantum of compensation due
More example sentences
  • Assessing his prospects of success in those claims and the quantum of any damages requires many of the underlying issues to be tested or tried.
  • Counsel for the plaintiffs submits that the quantum of damages should be assessed in the amount of $20,000.00 for each of the plaintiffs.
  • It points out at line 15 that the first matter to be determined on an application under the section is: the quantum of common law damages which would have been recoverable had they been sued for.
2.1A share or portion: each man has only a quantum of compassion
More example sentences
  • You would need to go the second step and, in addition, you would need to know the quantum of the shares.
  • Haryana has a sense of grievance at the non-completion of the SYL canal and the consequent non-availability of the quantum of waters allocated to it.
  • The quantum and the interest rate are not known, according to sources in the banking industry.


Mid 16th century (in the general sense 'quantity'): from Latin, neuter of quantus (see quantity). Sense 1 dates from the early 20th century.

  • Although you will often come across a sentence like ‘This product represents a quantum leap forward in telecommunications technology’, the curious thing about the term quantum leap is that, strictly speaking, it does not describe a large change at all, but a tiny one. Quantum comes from Latin quantus, ‘how big?’ or ‘how much?’, and originally meant ‘a quantity or amount’. In physics a quantum (a term introduced by the physicist Max Planck around 1900) is a very small amount of energy, the minimum amount of energy that can exist in a given situation, and a quantum jump is the abrupt change of an electron or atom from one energy state to another. Although this is a tiny jump in terms of size, it is an instantaneous and dramatic one, which explains why the term came into general usage from around 1970 to describe a sudden large increase or major advance. Quantity (Late Middle English) comes from the same root as quantum.

For editors and proofreaders

Line breaks: quan|tum

Share this entry

What do you find interesting about this word or phrase?

Comments that don't adhere to our Community Guidelines may be moderated or removed.