a tuft, as of grass, twigs, hair, or the like; especially, a dense tuft or bunch of grass or sedge.-same as tussock grass, below.-a caterpillar of any one of numerous species of bombycid moths. the body of these caterpillars is covered with hairs which form long tufts or brushes. some species are very injurious to shade and fruit trees. called also tussock caterpillar. see orgyia.