Nausea is having the feeling of unease and discomfort in your stomach. Sometimes feels like you have to vomit. An example sentence would be: "You might experience nausea after riding this roller-coaster." Nauseous is when you are affected by nausea. "I felt nauseous after riding that roller-coaster." Nauseating is something that can make you feel nauseous. "That roller-coaster ride was nauseating."