Definition of louse

• n. - Any one of numerous species of small, wingless, suctorial, parasitic insects belonging to a tribe (Pediculina), now usually regarded as degraded Hemiptera. To this group belong of the lice of man and other mammals; as, the head louse of man (Pediculus capitis), the body louse (P. vestimenti), and the crab louse (Phthirius pubis), and many others. See Crab louse, Dog louse, Cattle louse, etc., under Crab, Dog, etc.
• n. - Any one of numerous small mandibulate insects, mostly parasitic on birds, and feeding on the feathers. They are known as Mallophaga, or bird lice, though some occur on the hair of mammals. They are usually regarded as degraded Pseudoneuroptera. See Mallophaga.
• n. - Any one of the numerous species of aphids, or plant lice. See Aphid.
• n. - Any small crustacean parasitic on fishes. See Branchiura, and Ichthvophthira.
• v. t. - To clean from lice.