When you're aghast, you're shocked and horrified by something terrible or disturbing you've just seen or heard. Picture the expression on someone's face when they walk into a room and discover their little brother has drawn all over the walls with permanent marker, or when they learn that a trusted friend has been spreading cruel rumors. That wide-eyed, open-mouthed look of shock mixed with dismay: that's being aghast.

The word captures shock combined with horror or moral outrage. If someone tells you they're serving pizza for lunch, you might be pleasantly surprised. But if you see someone deliberately destroy another person's science fair project, you'd be aghast at such cruel behavior.

You'll often see this word used when people witness something that violates their sense of right and wrong, or when they hear about it happening.