Learner's definition of NINETY
the numbers ranging from 90 to 99
temperatures in the nineties
It was priced in the low nineties. [=its price was about $91,000–$93,000]
a set of years ending in digits ranging from 90 to 99
I studied there in the nineties. [=between 1990–1999]
During the nineties, he was going to college and working part-time.
He lived into his nineties. [=he was over ninety years old when he died]