When you see the adverb aback, it almost always follows the verb "to take." When you're taken aback, you're startled, often by another person's actions. If someone makes a rude comment at a dinner party, for example, you'll be taken aback. The word dates from about 1200, and it comes from the Old English on bæc, "at or on the back." It was first used as a nautical term for a strong wind flattening the sail against the ship's mast.