plural nineties
Definition of ninety
1
: a number equal to nine times 10 — see Table of Numbers
2
nineties plural
: the numbers 90 to 99
specifically
: the years 90 to 99 in a lifetime or century
She's in her nineties.
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Merriam-Webster unabridged
Share ninety
Time Traveler for ninety
The first known use of ninety was before the 12th century
See more words from the same century