louse

American  

[lous, lous, louz] / laʊs, laʊs, laʊz /

noun

plural

lice, louses

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 humanus body louse or Pediculus humanus capitis 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. plant louse.

4. Slang. a contemptible person, especially an unethical one.

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verb (used with object)

loused, lousing

1. to delouse.

verb phrase

1. louse up to spoil; botch.

   Miscasting loused up the movie.

louse British  

/ laʊs /

noun

1. any wingless bloodsucking insect of the order Anoplura: includes Pediculus capitis ( head louse ), Pediculus corporis ( body louse ), and the crab louse, all of which infest man

2. any wingless insect of the order Mallophaga, such as the chicken louse: external parasites of birds and mammals with biting mouthparts

3. any of various similar but unrelated insects, such as the plant louse and book louse

4. slang an unpleasant or mean person

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verb

1. to remove lice from

2. slang (foll by up) to ruin or spoil

Etymology

Origin of louse

First recorded before 900; 1910–15 louse for def. 4; Middle English lous(e), luse, plural lise, lice; Old English lūs, plural lȳs; cognate with Dutch luis, German Laus, Old Norse lūs

Explanation

A louse is a tiny insect that lives on the skin of animals and people. If you find a louse in your hair, you'll have to treat your scalp to get rid of any of its friends that might still be lurking there. Since they tend to travel in groups, the plural form of louse, lice, is much more common than the singular. Lice are small parasites that live on skin cells, blood, or other tiny bits of some host animal. If you're the host animal, you'll probably have an itchy head, and anyone who borrows your pillow or wears your hat will likely get lice too. A louse, informally, is also "an obnoxious person."

Example Sentences

Initially, we can’t wait for Iacono’s louse to get eaten but we come to treasure his comic relief, particularly when Xavier wanders off to relieve himself next to a nest of velociraptors.

From Los Angeles Times • Jun. 30, 2025

A genetic analysis based on louse DNA revealed the existence of two distinct clusters of lice that rarely interbred.

From Science Daily • Nov. 8, 2023

Along our evolutionary journey from monkey-like primates to bipedal apes to big-brained humans, we have had the company of an extraordinarily loyal companion: Pediculus humanus, otherwise known as the human louse.

From New York Times • Nov. 8, 2023

“We can see the louse DNA reflected in our own history.”

From Science Magazine • Nov. 7, 2023

I could see distinctly the limbs of these vermin with my naked eye, much better than those of a European louse through a microscope, and their snouts with which they rooted like swine.

From "The Invention of Science" by David Wootton