twen·ty 
(twĕntē, twŭn-)
(twĕntē, twŭn-)n.
1. The cardinal number equal to 2 × 10.
2. twenties
a. A decade or the numbers from 20 to 29: The children are now in their twenties. The temperature dipped into the twenties.
b. often Twenties The decade from 20 to 29 in a century.
3. A twenty-dollar bill.
[Middle English, from Old English twēntig; see dwo- in the Appendix of Indo-European roots.]
twenty adj. & pron.