To wince means to make a quick, involuntary movement or expression because something hurts, embarrasses you, or makes you uncomfortable. Your body reacts before you can stop it: you might scrunch up your face, pull back slightly, or tense your shoulders.

You wince when the doctor gives you a shot, when you remember something embarrassing you said yesterday, or when you hear the horrible screech of chalk on a chalkboard. You might wince watching a character in a movie make a terrible mistake, or when your friend tells a joke so bad it's actually painful to hear.

The key thing about wincing is that it's automatic. You don't decide to wince; your face and body just do it in response to something unpleasant. It's physical and visible, even when what bothers you is just a memory or thought. If you're watching someone attempt a dangerous skateboard trick, you might wince right before they fall, anticipating the pain even though it's not happening to you.

The word can be a noun too: “He gave a wince of pain when he stubbed his toe.”