n. pl. nine·ties
1. The cardinal number equal to 9 × 10.
a. A decade or the numbers from 90 to 99: My grandparents are in their nineties. During the heat wave, the temperature stayed in the nineties.
b. often Nineties The decade from 90 to 99 in a century.
[Middle English ninti, from Old English nigontig; see new in the Appendix of Indo-European roots.]
ninety adj. & pron.
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