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To expose something to fresh air (often to improve its scent). After I spilled water on the blanket, I put it on the back porch to air out. She opened all of the windows to let her house air out on the first day of spring. You need to air out your goalie pads before the next game—they stink!
[for something] to remain in the fresh air and become fresher. The pillows are airing out on the balcony.
air something out
to freshen something up by placing it in the open air; to freshen a room by letting outside air move through it. I'll have to air out the car. Someone has been smoking in it.