Nauseous means feeling sick to your stomach, like you might throw up. When you're nauseous, your stomach feels queasy and unsettled. You might feel nauseous after spinning in circles too many times, riding a roller coaster, eating food that's gone bad, or when you have the flu.

The word captures that unmistakable feeling when your stomach seems to be doing flips and you're not sure you can keep your lunch down. A bumpy car ride on a winding mountain road might make you feel nauseous. Some people feel nauseous when they're nervous, like before giving a big presentation.

Technically, something that causes nausea should be called nauseating, while someone experiencing the sick feeling is nauseated. A nauseating smell makes you feel nauseated. However, people commonly use nauseous for both meanings, and most dictionaries now accept “I feel nauseous” as correct. When in doubt, you can always say “I feel sick to my stomach,” and everyone will understand exactly what you mean.