For the American pronunciation: nah-tious.
For the British pronunciation: nah-zee-ous
I figure that this is a pretty useful word to know. After all, everyone feels sick at one point or another, and it may be a good idea to know how to describe your symptoms to a doctor or a friend.
Here are some more examples:
I often feel nauseous in the car, especially if the road twists and turns.
Just watching you eat that is making me nauseous.
Doctor: what are your symptoms?
Patient: I have a headache, a fever, and I feel nauseous.