ninety

noun
nine·​ty | \ ˈnīn-tē How to pronounce ninety (audio) \
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.