Etymology
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Middle Ages (n.)
"period between ancient and modern times" (formerly roughly 500-1500 C.E., now more usually 1000-1500), attested from 1610s, translating Latin medium aevum (compare German mittelalter, French moyen âge).
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Black Hills 
South Dakota landform, translating Lakhota pahá-sapa; supposedly so called because their densely forested flanks look dark from a distance.
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black market (n.)
"unauthorized dealing in restricted or rationed commodities," 1931, from black (adj.), probably suggesting "dark, invisible" or "shady, improper" + market (n.). As an adjective by 1935. It exploded in popularity with the coming of World War II rationing.
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Novus Ordo Seclorum 

on the Great Seal of the United States of America, apparently an allusion to line 5 of Virgil's "Eclogue IV," in an 18c. edition: Magnus ab integro seclorum nascitur ordo "The great series of ages begins anew." The seal's designer, Charles Thomson, wrote that the words "signify the beginnings of the New American Era." (see Annuit Coeptis).

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ice age (n.)
1855, from ice (n.) + age (n.). Perhaps translating German Eiszeit (1837). An earlier term in the same sense was glacial epoch (1841). Local scientific men had noticed from the late 18c. evidence that the Alpine glaciers once had been much larger; in the 1830s stray boulders, moraines, and polished bedrock in northern Europe (formerly interpreted as relics of catastrophic floods) began to be understood as revealing the former presence of a large ice cap there. When Agassiz, a convert to the theory, came to America in 1846 he found similar evidence in New England. The glacial theory and the notion that there had been several worldwide ice ages seems to have been generally accepted by the 1870s.
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black eye (n.)

"discoloration around the eye from injury" c. 1600, from black (adj.) + eye (n.). Figurative sense of "injury to pride, rebuff" is by 1744; that of "bad reputation" is from 1880s.

In reference to dark eyes, often as a mark of beauty, from 1660s. Black-eyed is from 1590s of women, of peas from 1728. The black-eyed Susan as a flower (various species) so called from 1881, for its appearance. It also was the title of a poem by John Gay (1685-1732), which led to a popular mid-19c. British stage play of the same name.

All in the Downs the fleet was moored,
  The streamers waving in the wind,
When black-eyed Susan came aboard,
  "Oh! where shall I my true love find?
Tell me, ye jovial sailors, tell me true,
If my sweet William sails among the crew?"
[etc.]
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