n. pl. thir·ties 1. The cardinal number equal to 3 × 10. 2. thirties 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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