Etymology
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cosine (n.)

one of the three fundamental functions of trigonometry,  1630s, contraction of co. sinus, abbreviation of Medieval Latin complementi sinus (see complement + sine). The word was used in Latin c. 1620 by English mathematician Edmund Gunter.

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arc (n.)

late 14c., "part of a curved line," originally in reference to the sun's apparent motion across the sky, from Old French arc "bow, arch, vault" (12c.), from Latin arcus "a bow, arch," from Proto-Italic *arkwo- "bow."

This has Germanic cognates in Gothic arhvazna, Old English earh, Old Norse ör "arrow," from Proto-Germanic *arkw-o- "belonging to a bow." It also has cognates in Greek arkeuthos, Latvian ercis "juniper," Russian rakita, Czech rokyta, Serbo-Croatian rakita "brittle willow." De Vaan sees an Italo-Germanic word for "bow" which can be connected with Balto-Slavic and Greek words for "willow" and "juniper" "under the well-founded assumption that the flexible twigs of juniper or willow were used as bows." The Balto-Slavic and Greek forms point to *arku-; "as with many plant names, this is likely to be a non-IE loanword."

The electrical sense is attested from 1821.

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arc (v.)

1882, in the electrical sense, from arc (n.). Meaning "to move in an arc" is attested by 1940. Related: Arced; arcing.

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arc-light (n.)

"light produced by an electric arc," 1871, from arc (n.) + light (n.). Related: Arc-lamp.

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arcuate (adj.)

"bent like a bow," 1620s, from Latin arcuatus "bow-like, arched," past participle of arcuare "to bend like a bow," from arcus "a bow" (see arc (n.)). Related: Arcuration.

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radian (n.)

"angle subtended at the center of a circle by an arc equal in length to the radius," 1879, from radius.

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klieg 

kind of arc lamp used as a studio light, 1921, from Bavarian-born U.S. engineers brothers Anton and John Kliegl, who invented it.

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arcade (n.)

1731, "vaulted space" (as arcado from 1640s), via French arcade, which probably is from Italian arcata "arch of a bridge," from arco "arc," from Latin arcus "a bow, arch" (see arc (n.)).

The English word was applied to passages formed by a succession of arches supported on piers or pillars, avenues of trees, and ultimately to any covered avenue (1731), especially one lined with shops (1795) or amusements; hence arcade game (1977).

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azimuth (n.)

"arc marking the distance of a star from the north or south point of the meridian," late 14c., from Old French azimut, from Arabic as-sumut "the ways," plural of as-samt "the way, direction" (see zenith). Related: Azimuthal.

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bloop (v.)

1926, a word from the early days of radio (see blooper). In baseball, "hit a ball in a high arc over the head of a fielder," by 1940. Related: Blooped; blooping. As a noun from 1931.

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