a cardinal number, 10 times 2.

a symbol for this number, as 20 or XX.

a set of this many persons or things.

Informal . a twenty-dollar bill

Can you give me two tens for a twenty?

twenties, the numbers, years, degrees, or the like, from 20 through 29, as in referring to numbered streets, indicating the years of a lifetime or of a century, or referring to degrees of temperature

He lives in the West Twenties. She's in her early twenties. The temperature must be in the high twenties today.

amounting to 20 in number.