Etymology
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hands-on (adj.)
by 1969, originally in reference to the use of computers in education; see hand (n.) + on (adv.).
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off-and-on (adv.)

"intermittently, occasionally," 1530s; see off (adv.) + on. As an adjective, "occasional," from 1580s.

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air-conditioner (n.)
from air (n.1) + conditioner. Along with air-conditioning first attested 1909, originally an industrial process in textile manufacturing. The word conditioning was applied to the determination of the moisture content of textiles, control of which was essential to spin fine cotton yarns. The original purpose of air-conditioning was to purify air and regulate moisture. In 1906 Stuart W. Cramer of Charlotte, N.C., and Willis H. Carrier of Buffalo, N.Y., independently devised methods of using a fine spray of water to cool air. Self-contained air-conditioning units, complete with refrigeration equipment, were widely used to cool air in U.S. stores, restaurants, etc. from the 1930s. An earlier name for such a device (using ice and fans) was air cooler (1875).
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air-freshener (n.)
1945, from air (n.1) + agent noun from freshen.
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air-raid (n.)

1914, from air (n.1) meaning "by aircraft" + raid (n.); originally in reference to British attacks Sept. 22, 1914, on Zeppelin bases at Cologne and Düsseldorf in World War I. The German word is Fliegerangriff "aviator-attack," and if Old English had survived into the 20th century our word instead might be fleogendeongrype.

One didn't dare to inhale for fear of breathing it in. It was the sound of eighteen hundred airplanes approaching Hamburg from the south at an unimaginable height. We had already experienced two hundred or even more air raids, among them some very heavy ones, but this was something completely new. And yet there was an immediate recognition: this was what everyone had been waiting for, what had hung for months like a shadow over everything we did, making us weary. It was the end. [Hans Erich Nossack, "Der Untergang," 1942]
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plein-air (adj.)
1894, from French phrase en plein air, literally "in the open air." The style developed among French impressionists c. 1870.
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air-bag (n.)

"sealed bag filled with air," 1836, from air (n.1) + bag (n.). In early use a means of raising sunken ships, etc.; as an automobile safety feature by 1970.

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air-brake (n.)
brake that works by compressed air power, 1872, from air (n.1) + brake (n.1). Related: Air-brakes.
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air-shaft (n.)
long narrow passage for admitting air, 1690s, from air (n.1) + shaft (n.2).
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air-brush (n.)
also airbrush, "atomizer used for spraying liquid ink or paint," 1883, from air (n.1) + brush (n.1). Invented a few years earlier but called at first paint distributer; renamed by U.S. manufacturer Liberty Walkup, who improved the design. As a verb by 1902. Related: Airbrushed; airbrushing.
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