—n. 1. any small, wingless insect of the order Anoplura (sucking louse), parasitic on humans and other mammals and having mouthparts adapted for sucking, as Pediculus humanus(body louse or head louse) and Phthirius pubis(crab louse or pubic louse). 2. any insect of the order Mallophaga (bird louse, biting louse, or chewing louse), parasitic on birds and mammals, having mouthparts adapted for biting.
3. See plant louse. 4. Slang.a contemptible person, esp. an unethical one.
—v.t. 1. to delouse.
2. louse up,Slang.to spoil; botch: Miscasting loused up the movie.