Etymology
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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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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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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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Leibnitz 
Gottfried Wilhelm Leibnitz (also Leibniz), 1646-1716, German philosopher and mathematician, independent inventor (Newton was the other) of differential and integral calculus.
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differentiation (n.)

1831 in calculus; 1855 as "action of differentiating, condition of being different," noun of action from differentiate. As "action of noting a difference," 1866.

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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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differential (adj.)
Origin and meaning of differential

1640s, "making or exhibiting a difference," from Medieval Latin differentialis, from Latin differentia "diversity, difference" (see difference). Related: Differentially. As a noun in mathematics, "an infinitesimal difference between two values of variable quantity," from 1704. Differential calculus is attested from 1702.

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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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saxifrage (n.)

type of plant typically found in cold regions and used medicinally, late 14c., from Old French saxifrage (13c.), from Late Latin saxifraga, name of a kind of herb, from Latin saxifraga herba, literally "a rock-breaking herb," from saxifragus "stonebreaking," from saxum "stone, rock" + frag-, root of frangere "to break" (from PIE root *bhreg- "to break"). Pliny says the plant was so called because it was given to dissolve gallstones, but a more likely explanation is that it was so called because it grows in crevices in rocks. (Latin used different words for "stone" and "gallstone" — saxum and calculus). Related: Saxifragaceous; saxifragal.

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