ninety

Ninety is a number between eighty and one hundred.

When we use the word "ninety" in everyday language, it's usually to talk about quantities or amounts. For example, if you have ninety dollars left on your gift card, that means you can spend nine tens of dollars before it runs out. People often say things like "I'm ninety percent sure I'll be there tomorrow" which is a way of estimating the likelihood of something happening. It's also common to hear people talking about their age in nineties – if someone says they're ninety years old, that means they've lived through nine decades!