n. pl. thir·ties
1. The cardinal number equal to 3 × 10.
a. A decade or the numbers from 30 to 39: They settled down in their thirties. The temperature fell into the thirties.
b. often Thirties The decade from 30 to 39 in a century.
3. An indication of the end of a news story, usually written 30.
4. Sports The second point that is scored by one side in tennis.
[Middle English thritty, thirty, from Old English thrītig; see trei- in the Appendix of Indo-European roots.]
thirty adj. & pron.
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