Etymology
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play-list (n.)

also playlist, 1975, "list of recordings to be played on the air by a radio station," from play (v.) + list (n.1).

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obambulation (n.)

"a walking about," c. 1600, from Latin obambulationem (nominative obambulatio) "a going or walking about," noun of action from past-participle stem of obambulare "to go or walk about, walk past, walk near," from ob "about" (see ob-) + ambulare "to walk, go about" (see amble (v.)).

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airborne (adj.)
also air-borne, 1640s, "carried through the air," from air (n.1) + borne. Of military units, from 1937.
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circumambulate (v.)

"to walk round or about," 1650s, from Latin circumambulatus, past participle of circumambulare "to walk around," from circum "around" (see circum-) + ambulare "to walk, go about" (see amble (v.)). Related: Circumambulated; circumambulating; circumambulation.

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airtight (adj.)
also air-tight, "impermeable to air," 1760, from air (n.1) + tight. Figurative sense of "incontrovertible" (of arguments, alibis, etc.) is from 1929.
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aerobic (adj.)
"able to live or living only in the presence of oxygen, requiring or using free oxygen from the air," 1875, after French aérobie (n.), coined 1863 by Louis Pasteur in reference to certain bacteria; from Greek aero- "air" (see aero-) + bios "life," from PIE root *gwei- "to live." Aerobian and aerobious also were used in English. Hence aerobe "type of micro-organism which lives on oxygen from the air." Meaning "pertaining to aerobics is from 1968.
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airline (n.)
also air-line, 1813, "beeline, straight line between two points on the earth's surface" (as through the air, rather than over terrain), from air (n.1) + line (n.). From 1853 and in later 19c. especially in reference to railways that ran directly between big cities in the U.S. instead of meandering from town to town in search of stock subscriptions as early railways typically did. Meaning "public aircraft transportation company" is from 1914.
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pad (v.1)

"to walk, travel on foot, tramp slowly or wearily along," 1550s, probably from Middle Dutch paden "walk along a path, make a path," from pad, pat "path" (compare path). Originally a cant word among criminals and vagabonds, perhaps of imitative origin (sound of feet trudging on a dirt road). Related: Padded; padding. English also formerly had the noun pad meaning "path, foot path" (1560s), which might be from this verb, or from the Dutch noun, or a variant of path.

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ambulate (v.)
"to walk, move about," 1620s, from Latin ambulatus, past participle of ambulare "to walk, go about" (see amble (v.)). Related: Ambulated; ambulating.
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aerodrome (n.)
1902, "hangar for airships," from aero- on analogy of hippodrome. From 1909 as "airport." Earlier (1891) a name for a flying machine, from Greek aerodromos "a running through the air."
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