Etymology
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quantity (n.)

early 14c., quantite, "amount, magnitude, the being so much in measure or extent," from Old French quantite, cantite (12c., Modern French quantité) and directly from Latin quantitatem (nominative quantitas) "relative greatness or extent," coined as a loan-translation of Greek posotes (from posos "how great? how much?") from Latin quantus "of what size? how much? how great? what amount?," correlative pronominal adjective (from PIE root *kwo-, stem of relative and interrogative pronouns).

From late 14c. as "that which has quantity, a concrete quantity;" from 1610s in the concrete sense of "an object regarded as more or less." In prosody and metrics, "the relative time occupied in uttering a vowel or syllable" (distinguishing it as long or short) by 1560s. Latin quantitatem also is the source of Italian quantita, Spanish cantidad, Danish and Swedish kvantitet, German quantitat.

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quantitation (n.)

"action of ascertaining the quantity of," 1952, from quantity + -ation, ending used in forming nouns of action. Related: Quantitate (v.), 1960.

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quantitive (adj.)

a rare variant of quantitative, 1650s, from quantity + -ive. Related: Quantitively.

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quantitative (adj.)

1580s, "having quantity," from Medieval Latin quantitativus, from stem of Latin quantitas (see quantity). Meaning "measurable" is from 1650s. Related: Quantitatively; quantitativeness.

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quantify (v.)

c. 1840, in logic, "make explicit the use of a term in a proposition by attaching all, some, etc.," from Modern Latin quantificare, from Latin quantus "as much," correlative pronominal adjective (see quantity) + combining form of facere "to make" (from PIE root *dhe- "to set, put"). Literal sense of "determine or mark the quantity of, measure" is by 1878. Related: Quantified; quantifying.

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quantum (n.)

1610s, "sum, amount," from Latin quantum (plural quanta) "as much as, so much as; how much? how far? how great an extent?" neuter singular of correlative pronominal adjective quantus "as much" (see quantity).

The word was introduced in physics directly from Latin by Max Planck, 1900, on the notion of "minimum amount of a quantity which can exist;" reinforced by Einstein, 1905. Quantum theory is from 1912; quantum mechanics, 1922. The term quantum jump "abrupt transition from one stationary state to another" is recorded by 1954; quantum leap "sudden large advance" (1963), is often figurative.

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*kwo- 
also *kwi-, Proto-Indo-European root, stem of relative and interrogative pronouns.

It forms all or part of: cheese (n.2) "a big thing;" cue (n.1) "stage direction;" either; hidalgo; how; kickshaw; neither; neuter; qua; quality; quandary; quantity; quasar; quasi; quasi-; query; quib; quibble; quiddity; quidnunc; quip; quodlibet; quondam; quorum; quote; quotidian; quotient; ubi; ubiquity; what; when; whence; where; whether; which; whither; who; whoever; whom; whose; why.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit kah "who, which;" Avestan ko, Hittite kuish "who;" Latin quis/quid "in what respect, to what extent; how, why," qua "where, which way," qui/quae/quod "who, which;" Lithuanian kas "who;" Old Church Slavonic kuto, Russian kto "who;" Old Irish ce, Welsh pwy "who;" Old English hwa, hwæt, hwær, etc.
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quantification (n.)

"act of attaching quantity to; act of determining the quantity," 1847, noun of action from quantify. Related: Quantificational.

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minus (n.)

1650s, "the minus sign," from minus (prep.). From 1708 as "a negative quantity, a quantity subtracted."

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Coulomb (n.)

"unit of quantity in measuring electric current" (the quantity of electricity conveyed in 1 second by a current of 1 ampere, 1881, named for French chemist Charles-Augustin de Coulomb (1736-1806), who devised a method of measuring electrical quantity. The surname is a French form of Columbus.

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