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Word Unpacked.

quantum

noun [ˈkwɑntəm]
pronunciation CMU Pronouncing Dictionary, open source

A quantum is the smallest separate amount in which something such as energy can exist or change; in legal and older English it simply means an amount.

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Definitions

  1. In physics, the smallest fixed unit of a quantity such as energy, which can only be gained or lost in whole units of that size.
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  2. A quantity or amount of something, especially a share or sum that has to be settled or measured.
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  3. As a modifier, connected with the physics of very small particles, as in quantum theory or quantum computer.
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Examples

Usage

Quantum has two lives in English. In science it names a tiny, indivisible step of energy or another physical quantity, and it often works like an adjective in phrases such as quantum mechanics, quantum state and quantum computing. In law and formal writing it keeps its older meaning of an amount, so lawyers speak of the quantum of damages or the quantum of proof without any link to physics.

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The plural is quanta, taken over from Latin, although quantums appears in informal use and is usually avoided in careful writing. When quantum stands before another noun it does not change, so a single device is a quantum computer and several are quantum computers. Related words include quantize, meaning to divide into fixed steps, and quantal, a rarer adjective used in some technical fields.

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The everyday phrase quantum leap means a sudden and very large change or advance, as in a quantum leap in safety. This is a little ironic, because in physics a quantum jump is extremely small; the phrase stresses the suddenness of the change rather than its size. Writers who want to avoid the cliché can use major breakthrough or dramatic improvement instead.

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Word forms

Forms according to English morphology, plural quanta as given by Webster 1913 (editorial description).

word forms

przypadek forma
singular quantum
plural quanta

Word forms: Webster's Revised Unabridged Dictionary, 1913 · source

Collocations

Synonyms · Antonyms

Synonyms amount, quantity, portion, unit
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Etymology

From Latin quantum, the neuter form of quantus, meaning how great or how much. Webster links the word to quantity and records the plural quanta, a mathematical sense of a definite portion limited by a boundary, and the legal phrase quantum meruit, Latin for as much as he merited.
source Webster's Revised Unabridged Dictionary, 1913, open source

Related words

Related entries

Questions and answers

What does quantum mean in simple terms?

In science it means the smallest possible packet of something, most often energy. Instead of flowing smoothly, energy at the level of atoms comes in these fixed packets. Outside science the word can also just mean an amount, which is how it is used in law.

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What is the plural of quantum?

The standard plural is quanta, as in energy quanta. The form quantums turns up now and then, but most editors treat it as a mistake. In compounds such as quantum computer the word does not take a plural ending at all.

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Is a quantum leap big or small?

In everyday English a quantum leap is a big, sudden step forward. In physics a quantum jump is tiny. Both meanings share the idea of a sudden change from one level to another with nothing in between, which explains how the phrase moved into ordinary speech.

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Where does the word quantum come from?

It comes from Latin quantus, meaning how great or how much, the same root that gave English the word quantity. The 1913 edition of Webster gives it with the plural quanta and with legal and mathematical senses.

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