Queasy describes a feeling of nervousness, uneasiness, or anxiety. If you're queasy about making a speech in front of the entire high school, you have a feeling that it won't go well.
Queasy can also mean feeling sick to your stomach. If you eat a sandwich made of turkey that expired two months ago, you'll likely feel queasy and throw up. If you feel queasy during a flight, both meanings of the word can apply: you may be queasy — as in anxious — because you're afraid of flying. And you may also be queasy — as in sick to your stomach — as a result of the air turbulence.