1. the years from 1990 to 1999
Usage: often used with ‘the’
2. the years from 90 to 99 in any century
3. the range of temperatures from 90 to 99 degrees

Examples

• She grew up in the nineties listening to grunge music.
• The nineties were a decade of rapid technological change.
• My grandmother is in her nineties but still very active.
• The temperature reached the nineties yesterday.
• Fashion from the nineties is making a comeback.
• He was born in the early nineties.
• The heat wave brought temperatures into the upper nineties.