To unnerve someone means to make them lose their confidence or courage, causing them to feel anxious, shaken, or uncertain. It's that feeling when something disturbs your calm so much that you can't think straight or act normally.

Imagine standing in front of the class ready to give a presentation you've practiced many times. You feel prepared and confident. Then you notice the principal has walked in to observe, and suddenly your mind goes blank. That's being unnerved: something unexpected has shaken your composure.

The word suggests more than simple nervousness. When you're unnerved, something has rattled you or thrown you off balance. A strange noise in an empty house might unnerve you. A teacher's unexpected pop quiz might unnerve even the best students. Athletes talk about opponents trying to unnerve them with trash talk or intimidation, hoping they'll make mistakes.