/nuyn"tee/ , n. , pl. nineties , adj.
n.
1. a cardinal number, ten times nine.
2. a symbol for this number, as 90 or XC.
3. a set of this many persons or things.
4. nineties , the numbers, years, degrees, or the like, from 90 through 99, as in referring to numbered streets, indicating the years of a lifetime or of a century, or degrees of temperature: His grandmother is in her nineties.
adj.
5. amounting to 90 in number.
[ bef. 1000; ME nineti, OE nigontig. See NINE, -TY 1 ]