louse
/lous/
noun
  1. Any of numerous small, flat-bodied, wingless biting or sucking insects of the order Phthiraptera, which live as external parasites on birds and mammals, including humans. The lice are sometimes classified together with the psocids in the order Psocodea.
  2. (Slang) A mean or despicable person.
from The American Heritage® Dictionary of the English Language, 5th Edition. More at Wordnik

A louse is a common derogatory term to describe a person who acts like a parasite, a pest, or someone extremely unpleasant.
Merriam-Webster offers this example: Her ex-husband is a real louse.

D.C states: Slang meaning "obnoxious person" is from 1630s; to louse up "ruin, botch" first attested 1934.

The earliest instance of the phrase louse around I found in Google books was American Dialect Society, 1927

v. phr. To loiter about aimlessly. Also, Laze around.

Which suggests that the term was not as derogatory as it is today. The better-known idiom, to lounge around, is but another way of saying to laze around. The following excerpt confirms this meaning.

From 1931 Shoe the Wild Mare by Gene Fowler

Nowadays however, the idiom expresses contempt and suggests a parasitic approach to life. Wikitionary says

  1. (UK) To slack off; be lazy; be a "parasite" to someone/something.
Answer from Mari-Lou A on Stack Exchange
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Merriam-Webster
merriam-webster.com › dictionary › louse
LOUSE Definition & Meaning - Merriam-Webster
: a small usually sluggish arthropod (such as a head louse) that lives on other animals or on plants and sucks their blood or juices ... Noun a problem with head lice Her ex-husband is a real louse.
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Vocabulary.com
vocabulary.com › dictionary › louse
Louse - Definition, Meaning & Synonyms | Vocabulary.com
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."
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Encyclopedia Britannica
britannica.com › dictionary › louse
Louse Definition & Meaning | Britannica Dictionary
LOUSE meaning: 1 : a type of small insect that lives on the bodies of people or animals; 2 : a bad or cruel person
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Oxford Learner's Dictionaries
oxfordlearnersdictionaries.com › us › definition › english › louse_1
louse noun - Definition, pictures, pronunciation and usage notes | Oxford Advanced Learner's Dictionary at OxfordLearnersDictionaries.com
(plural louses) (informal, disapproving) a very unpleasant person · Steve had let her down; she should never have trusted the louse. Word OriginOld English lūs, (plural) lȳs, of Germanic origin; related to Dutch luis, German Laus.See louse in the Oxford Advanced American Dictionary ·
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Dictionary.com
dictionary.com › browse › louse
LOUSE Definition & Meaning | Dictionary.com
any insect of the order Mallophaga bird louse, biting louse, or chewing louse, parasitic on birds and mammals, having mouthparts adapted for biting. ... Slang. a contemptible person, especially an unethical one.
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Wiktionary
en.wiktionary.org › wiki › louse
louse - Wiktionary, the free dictionary
From Middle English lous, lows, ... Psocodea. (colloquial, dated, not usually used in plural form) A contemptible person; one who is deceitful or causes harm....
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Etymonline
etymonline.com › word › louse
Louse - Etymology, Origin & Meaning
parasitic insect infesting human ... Laus), from PIE *lus- "louse" (source also of Welsh lleuen "louse"). The meaning "obnoxious person" is from 1630s....
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Merriam-Webster
merriam-webster.com › thesaurus › louse
LOUSE Synonyms: 110 Similar and Opposite Words | Merriam-Webster Thesaurus
as in bastard a person whose behavior is offensive to others I can't believe you're willing to spend time with that lying louse
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YourDictionary
yourdictionary.com › home › dictionary meanings › louse definition
Louse Definition & Meaning | YourDictionary
To remove lice from the body of a person or animal; to delouse. ... From Middle English lows(e), from Old English lÅ«s, from Proto-Germanic *lÅ«s (cf. West Frisian lûs, Dutch luis, Low German Luus, German Laus), from Proto-Indo-European *lewH- (cf. Welsh llau (“lice"), Tocharian B luwo, maybe Sanskrit यूका (yÅ«kā)). ... The female louse lays around 6 eggs a day, firmly attached to the hair shaft close to the scalp. In shape it is ...
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Quora
quora.com › How-do-you-think-the-etymology-of-the-word-louse-reflects-its-historical-significance-and-cultural-impact
How to think the etymology of the word 'louse' reflects its historical significance and cultural impact - Quora
Answer (1 of 2): An interesting question ,and one I haven't given an answer to in many years, a louse,as you might already know,is a parasitic insect, such as lice,when we say we got a lousy deal,or they are a lousy person ,we are referring to a distinctive lack of any admirable qualities, just a...
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WordReference
wordreference.com › english dictionary › louse
louse - WordReference.com Dictionary of English
louse - WordReference English dictionary, questions, discussion and forums. All Free.
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TheFreeDictionary.com
thefreedictionary.com › louse
Louse - definition of louse by The Free Dictionary
Define louse. louse synonyms, louse pronunciation, louse translation, English dictionary definition of louse. n. 1. pl. lice Any of numerous small, flat-bodied, wingless biting or sucking insects of the order Phthiraptera, which live as external parasites on birds...
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Britannica Kids
kids.britannica.com › kids › article › louse › 609704
louse - Kids | Britannica Kids | Homework Help
The human louse (plural: lice) is a parasitic insect. A parasite is a living thing that depends on another living thing for its survival. Human lice attach to humans and feed…
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CDC
cdc.gov › dpdx › pediculosis › index.html
CDC - DPDx - Pediculosis
Adults: The adult louse is about the size of a sesame seed, has 6 legs (each with claws), and is tan to grayish-white . In persons with dark hair, the adult louse will appear darker. Females are usually larger than males and can lay up to 8 nits per day. Adult lice can live up to 30 days on a person’s head.
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CDC
cdc.gov › lice › about › index.html
About Lice | Lice | CDC
September 4, 2024 - Lice are parasites, or insects, found on people's heads and bodies, including the pubic area. Human lice survive by feeding on human blood. Infestation or infested person means that a person has lice. There are different types of lice on areas of the body. The three types of lice that live on humans are: ... Only the body louse can spread disease.