(~es)
1.
A ~ is a box outside your house where your letters are delivered. (AM)
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2.
A ~ is a metal box in a public place, where you put letters and packets to be collected. They are then sorted and delivered. (mainly AM; in BRIT, use post box )
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3.
On a computer, your ~ is the file where your e-mail is stored.
N-COUNT: usu sing