nineties
When you talk about the nineties, you are referring to numbers between 90 and 99. For example, if you are in your nineties, you are aged between 90 and 99. If the temperature is in the nineties, the temperature is between 90 and 99 degrees.
By this time she was in her nineties and needed help more and more frequently.
到这时她已经九十多岁了,越来越频繁地需要帮助。
The nineties is the decade between 1990 and 1999.
These trends only got worse as we moved into the nineties.
当我们步入20世纪90年代,这些潮流变得更糟了。
Ninety is the number 90.
It was decided she had to stay another ninety days.
经决定,她必须再呆九十天。