Affected or pretentious behavior intended to impress others. Can also refer to melodies or the plural of 'air' meaning atmosphere.
From Old French 'aire' meaning 'manner, appearance'. The sense of pretentious behavior developed in the 17th century from the idea of putting on artificial mannerisms like changing one's 'air' or demeanor.
The phrase 'putting on airs' captures how we literally change our atmosphere - just as air surrounds us invisibly, affected behavior creates an artificial social atmosphere that others can sense even if they can't quite name it.
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