Etymology
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base (n.)

"bottom of anything considered as its support, foundation, pedestal," early 14c., from Old French bas "depth" (12c.), from Latin basis "foundation," from Greek basis "a stepping, a step, that on which one steps or stands, pedestal," from bainein "to go, walk, step" (from PIE root *gwa- "to go, come").

The military sense of "secure ground from which operations proceed" is attested from 1860. The chemical sense of "compound substance which unites with an acid to form a salt" (1810) was introduced in French 1754 by French chemist Guillaume-François Rouelle (1703-1770).

The sporting sense of "starting point" is from 1690s, also "destination of a runner" (1812). As a "safe" spot in a tag-like or ball game, it is suggested from mid-15c. (as the name of the game later called prisoner's base). Hence baseball, base-runner (1867), base-hit (1874), etc. The meaning "resources on which something draws for operation" (as in power-base, database, etc.) is by 1959.

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base (v.)

1580s, transitive, "make or serve as a foundation for;" by 1841, of arguments, etc., "place (on or upon) a foundation," from base (n.). Related: Based; basing.

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base (adj.)

late 14c., "low, of little height," from Old French bas "low, lowly, mean," from Late Latin bassus "thick, stumpy, low" (used only as a cognomen in classical Latin, humilis being there the usual word for "low in stature or position"), possibly from Oscan, or Celtic, or related to Greek basson, comparative of bathys "deep."

The meaning "low on the social scale" is from late 15c.; that of "low in the moral scale" is attested by 1530s in English. The meaning "benefiting an inferior person or thing, unworthy" is from 1590s. Base metals (c. 1600) were worthless in contrast to noble or precious metals. Related: Basely.

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air (n.3)

"melody, tune, connected rhythmic succession of distinct musical sounds," 1580s, nativized from Italian aria (see aria), perhaps via French.

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air (n.1)

c. 1300, "invisible gases that surround the earth," from Old French air "atmosphere, breeze, weather" (12c.), from Latin aer "air, lower atmosphere, sky," from Greek aēr (genitive aeros) "mist, haze, clouds," later "atmosphere" (perhaps related to aenai "to blow, breathe"), which is of unknown origin. It is possibly from a PIE *awer- and thus related to aeirein "to raise" and arteria "windpipe, artery" (see aorta) on notion of "lifting, suspended, that which rises," but this has phonetic difficulties.

In Homer mostly "thick air, mist;" later "air" as one of the four elements. Words for "air" in Indo-European languages tend to be associated with wind, brightness, sky. In English, air replaced native lyft, luft (see loft (n.)). In old chemistry, air (with a qualifying adjective) was used of any gas.

To be in the air "in general awareness" is from 1875; up in the air "uncertain, doubtful" is from 1752. To build castles in the air "entertain visionary schemes that have no practical foundation" is from 1590s (in 17c. English had airmonger "one preoccupied with visionary projects"). Broadcasting sense (as in on the air, airplay) is by 1927. To give (someone) the air "dismiss" is from 1900. Air pollution is attested by 1870. Air guitar is by 1983. Air traffic controller is from 1956.

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air (n.2)

1590s, "manner, appearance" (as in an air of mystery); 1650s, "assumed manner, affected appearance" (especially in phrase put on airs, 1781), from French air "look, appearance, mien, bearing, tone" (Old French aire "reality, essence, nature, descent, extraction" (12c.); compare debonair), which is perhaps from Latin ager "place, field, productive land" (from PIE root *agro- "field") on the notion of "place of origin."

But some French sources connect this Old French word with the source of air (n.1), and it also is possible these senses in English developed from or were influenced by air (n.1); compare sense development of atmosphere and Latin spiritus "breath, breeze," also "high spirit, pride," and the extended senses of anima.

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air (v.)

1520s, "expose to open air," 1520s, from air (n.1). Figurative sense of "expose ostentatiously, make public" is from 1610s of objects, 1862 of opinions, grievances, etc. Meaning "to broadcast" (originally on radio) is from 1933. Related: Aired; airing.

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off-base (adv.)

"unawares," by 1936, American English, from off (adv.) + base (n.); a figurative extension from baseball sense of a runner being "not in the right position" (1882) and vulnerable to being picked off.

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mid-air (n.)

also midair, "the part of the air between the clouds and the air near the ground," from mid (adj.) + air (n.1).

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hot air (n.)

"unsubstantiated statements, boastful talk," 1900, from hot (adj.) + air (n.1). The adjectival phrase hot-air (of balloons, etc.) is from 1813.

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