Arrowroot is a plant that's used to make a cooking starch also called arrowroot. Some soups and puddings are thickened with arrowroot.
The plant known as arrowroot has small white flowers and fruit that resembles currants. Arrowroot is primarily grown for its root, though, which is washed, peeled, and beaten until all the starchy liquid comes out. When this liquid dries completely, it's the white powder you can find in the supermarket labeled arrowroot. The name allegedly comes from an old medicinal use of arrowroot, drawing poison from dart or arrow wounds.