Etymology
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calcitrant (adj.)
"kicking (at restrictions), refractory," 1857, as if from Latin calcitrantem (nominative calcitrans) "kicking" (see recalcitrant). Pedantic humor; probably a back-formation.
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calcium (n.)

metallic element, coined 1808 by English chemist Sir Humphry Davy, who first succeeded in isolating it, from Latin calx (genitive calcis) "limestone" (see chalk (n.)) + metallic element ending -ium. Related: Calcic.

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calculate (v.)
1560s, "to ascertain by computation, estimate by mathematical means," from Latin calculatus, past participle of calculare "to reckon, compute," from calculus (see calculus). Meaning "to plan, devise" is from 1650s; hence "to purpose, intend" and "to think, guess" (1830), both U.S. idioms. Replaced earlier calculen (mid-14c.), from Old French calculer. Related: Calculable.
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calculated (adj.)
1722, "suited, apt;" 1796, "devised beforehand;" past-participle adjective from calculate (v.). Related: Calculatedly.
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calculating (n.)
1710, "calculation," verbal noun from calculate (v.). Calculating-machine "mechanical computer, machine which performs mathematical calculations" is from 1830 [Babbage].
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calculating (adj.)
1710, "carrying out calculations," present-participle adjective from calculate (v.). Meaning "given to forethought and shrewdly or selfishly seeking advantage, scheming," is attested from 1802.
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calculation (n.)

late 14c., "art, manner, or practice of computing by numbers," also "the process of making a horoscope," from Late Latin calculationem (nominative calculatio) "a computation, calculation, reckoning," noun of action from past-participle stem of calculare "to reckon, compute," from Latin calculus "reckoning, account," originally "pebble used in counting," diminutive of calx (genitive calcis) "limestone" (see chalk (n.)). From early 15c. as "the result of reckoning, the solution for a problem."

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calculator (n.)

late 14c., "mathematician, one who calculates," from Latin calculator, from calculatus, past participle of calculare "to reckon, compute," from calculus "reckoning, account" (see calculus). Of mechanical adding machine contraptions, from 1784. Of electronic ones, from 1946.

Electronic calculator uses 18,000 tubes to solve complex problems [Scientific American headline, June 1946]
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calculous (adj.)
c. 1600, "of or pertaining to a bodily concretion;" 1670s, "stony, stone-like;" from Latin calculosus and (in the medical sense) directly from calculus "a pebble," diminutive of calx (genitive calcis) "limestone" (see chalk (n.)).
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calculus (n.)
mathematical method of treating problems by the use of a system of algebraic notation, 1660s, from Latin calculus "reckoning, account," originally "pebble used as a reckoning counter," diminutive of calx (genitive calcis) "limestone" (see chalk (n.)). Modern mathematical sense is a shortening of differential calculus.

In medicine, the word also has been used from 1732 to mean kidney stones, etc., then generally for "concretion occurring accidentally in the animal body," such as dental plaque.
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