To waggle means to move something back and forth with quick, short movements. When a dog wags its tail, it's waggling it rapidly from side to side. You might waggle your loose tooth with your tongue, or waggle your pencil between your fingers while thinking hard about a problem.

The word suggests playful, somewhat silly movement. A golfer waggles the club before swinging, making tiny adjustments to get the feel just right. Someone telling a funny story might waggle their eyebrows to add emphasis. Parents sometimes waggle their fingers at babies to make them giggle.

Waggle is closely related to wag, but waggle implies more energetic, repeated motion. A tail wags, but it waggles when the dog is especially excited. The word itself sounds like what it describes: loose, bouncy, and a little bit goofy. When something waggles, it doesn't move in a straight line or with dignity. It wobbles and jiggles with cheerful energy.