To flabbergast someone means to shock or surprise them so completely that they're left speechless or stunned. When you're flabbergasted, you're so amazed or bewildered that you can barely process what just happened.

Picture finding out that your quiet classmate secretly speaks five languages, or learning that your family is moving to another country next month. That jaw-dropping, can't-believe-it feeling is being flabbergasted. You might stand there with your mouth hanging open, unable to form words, your mind racing to catch up with the surprising news.

The word works for both wonderful and terrible surprises. A magician might flabbergast an audience by making an elephant disappear. A student might be flabbergasted to discover they won a national writing contest. A teacher might look flabbergasted when the class throws her a surprise retirement party.

The word itself sounds a bit silly and old-fashioned, which somehow makes it perfect for describing that particular feeling of being completely bowled over by surprise. When something merely surprises you, you might raise your eyebrows. When something flabbergasts you, you're left standing there wondering if what just happened was even real.