- any of an order (Anoplura) of small, flat, wingless insects with sucking mouthparts, parasitic on the skin or hair of humans and some other mammals; esp., the human body louse (Pediculus humanus corporis) and head louse (P. h. capitis)
- any of various arthropods that suck blood or juice from other animals or plants
- bird louse
- any of various other small insects, arachnids, and crustaceans that are not parasitic, as the book louse or wood louse
- Informal a person regarded as mean, contemptible, etc.
Origin of louseMiddle English lous from Old English lus (pl. lys), akin to German laus from Indo-European an unverified form l?s from source Welsh lleuen, Breton laouen
transitive verbloused, lous′ing