quantum

American  

[kwon-tuhm] / ˈkwɒn təm /

noun

quanta plural

1. quantity or amount.

   the least quantum of evidence.

2. a particular amount.

3. a share or portion.

4. a large quantity; bulk.

5. Physics.

   1. the smallest quantity of radiant energy, equal to Planck's constant times the frequency of the associated radiation.

   2. the fundamental unit of a quantized physical magnitude, as angular momentum.

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adjective

1. sudden and significant.

   a quantum increase in productivity.

quantum British  

/ ˈkwɒntəm /

noun

1. physics

   1. the smallest quantity of some physical property, such as energy, that a system can possess according to the quantum theory

   2. a particle with such a unit of energy

2. amount or quantity, esp a specific amount

3. (often used with a negative) the least possible amount that can suffice

   there is not a quantum of evidence for your accusation

4. something that can be quantified or measured

5. (modifier) loosely, sudden, spectacular, or vitally important

   a quantum improvement

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quantum Scientific  

/ kwŏn′təm /

quanta plural

1. A discrete, indivisible manifestation of a physical property, such as a force or angular momentum. Some quanta take the form of elementary particles; for example, the quantum of electromagnetic radiation is the photon, while the quanta of the weak force are the W and Z particles.

2. See also quantum state

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Other Word Forms

Inflected Forms

noun

• quanta
  plural

Etymology

Origin of quantum

1610–20; noun use of neuter of Latin quantus how much

Explanation

While quantum refers to a general quantity or size, it is most often used in physics as a measure of the smallest amount of something — usually energy — that something can possess. The plural form is quanta. In the 17th century, the word quantum, from the Latin word for "how much," referred to a portion. Quantum is usually a noun referring to a specific amount of something. However, it can also be used as an adjective, as in the phrase "quantum leap," where it refers to a sudden, important change. Outside of physics, the word might be used with "not" to refer to something insignificant, as in "There's not a quantum of truth in what you say."

Example Sentences

The government has taken stakes in startups like Kraken, Wayve and Oxford Quantum Circuits in recent weeks, in a bid to prevent them from moving out of the country to look for funding.

From The Wall Street Journal • Jun. 10, 2026

"It is alleged that more than 10 suspects were dropped off by a white Toyota Quantum near a petrol station in Cleveland," the police said in a statement.

From BBC • Jun. 10, 2026

The U.K. government has in recent weeks taken stakes in startups like Kraken—the technology arm of utility Octopus Energy—, self-driving car firm Wayve and quantum-computing company Oxford Quantum Circuits.

From The Wall Street Journal • Jun. 10, 2026

Quantum computing remains a speculative investment, with Quantinuum and peers yet to broadly commercialize technology.

From Barron's • Jun. 5, 2026

"Quantum theory is very worthy of regard," he observed politely, but he really didn’t like it.

From "A Short History of Nearly Everything" by Bill Bryson