To boggle means to overwhelm someone's mind with surprise, confusion, or amazement. When something boggles you, it's so unexpected or hard to understand that your brain almost stops working for a moment. You might say “It boggles my mind that the universe has no edge” or “The size of a blue whale boggles the imagination.”

The word captures that stunned feeling when you encounter something that seems impossible to grasp. Learning that there are more stars in the universe than grains of sand on all Earth's beaches boggles most people. When your friend claims to have read 500 books in a year, you might say “That boggles my mind!” You're expressing that the claim is so extreme it's hard to process.

Boggle is also the name of a popular word game where players search for words in a grid of letter cubes. The game earned its name because it challenges and puzzles players' minds. When you boggle at something, you're experiencing that same sense of mental challenge, except you're confronting something genuinely astonishing rather than a tricky puzzle.