A chock is a wedge or block placed against something to keep it from moving. Airplane mechanics slide chocks under the wheels of parked aircraft so they can't roll away. Truck drivers use chocks when loading cargo so their vehicles stay put. Chocks are usually made of wood, rubber, or metal, shaped like triangles or wedges that grip the ground and press against whatever needs to stay still.

The word appears in the phrase chock-full, which means completely full or packed tight. If your backpack is chock-full of books, you can't fit anything else inside. If a story is chock-full of action, exciting things happen constantly from beginning to end.

Think of how a chock works: it fills the space so completely that nothing can move. That's why chock-full suggests the same idea of being so packed that there's no room left. Whether you're securing a vehicle with chocks or describing a museum chock-full of fascinating exhibits, the word captures that sense of being firmly held in place or absolutely filled up.