Etymology
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micro- 

word-forming element meaning "small in size or extent, microscopic; magnifying;" in science indicating a unit one millionth of the unit it is prefixed to; from Latinized form of mikros, Attic form of Greek smikros "small, little, petty, trivial, slight," perhaps from PIE *smika, from root *smik- "small" (source also of Old High German smahi "littleness"), but Beekes thinks it a Pre-Greek word.

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nephron (n.)

"a filtration unit of the kidney," 1932, from German nephron (1924), from Greek nephros "kidney" (see nephro-).

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astronomical (adj.)

1550s, "pertaining to astronomy," from astronomy + -ical. The popular meaning "immense, concerning very large figures" (as sizes and distances in astronomy) is attested from 1899. Astronomical unit (abbreviation A.U.) "mean distance from the Earth to the Sun," used as a unit of measure of distance in space, is from 1909. Related: Astronomically.

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liter (n.)
unit of capacity in the metric system, 1797, from French litre (1793), from litron, name of an obsolete French measure of capacity for grain (16c.), from Medieval Latin litra, from Greek litra "pound" (unit of weight), which apparently is from the same Sicilian Italic source as Latin libra (see Libra).
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Newton (n.)

unit of force, 1904, named in honor of Sir Isaac Newton (1642-1727). Related: Newtonian.

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sucre (n.)
monetary unit of Ecuador, 1886, named for Antonio José de Sucre (1795-1830), Venezuelan general and liberator of Ecuador.
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luminaire (n.)
electric lighting unit, 1921, a trade term, from French luminaire, from Old French luminarie "lamp, candle; brightness, illumination" (see luminary).
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REM (n.1)

also R.E.M., rem, unit for measuring ionizing radiation, 1947, acronym of roentgen equivalent man.

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mark (n.2)

"unit of money or weight," late Old English marc, a unit of weight (chiefly for gold or silver) equal to about eight ounces, probably from Old Norse mörk "unit of weight," cognate with German Mark and probably ultimately a derivative of mark (n.1), perhaps in a sense of "imprinted weight or coin." It was a unit of account in England into 18c., perhaps originally introduced by the Danes, but never the name of a particular coin.

The word is found in all the Germanic and Romanic languages (compare Old Frisian merk, Dutch mark, Medieval Latin marca, French marc (11c.), Spanish and Italian marco); in English it was used from 18c. in reference to various continental coinages, especially the silver money of Germany first issued 1875.

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caddy (n.)
"small box for tea," 1792, from catty (1590s), Anglo-Indian unit of weight, from Malay (Austronesian) kati, a unit of weight. The catty was adopted as a standard mid-18c. by the British in the Orient and fixed in 1770 by the East India Company at a pound and a third. Apparently the word for a measure of tea was transferred to the chest it was carried in.
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