noun (1)
\ ˈlün How to pronounce loon (audio) \

Definition of loon

 (Entry 1 of 2)

1 : lout, idler
2 chiefly Scotland : boy
3a : a crazy person
b : simpleton


noun (2)

Definition of loon (Entry 2 of 2)

: any of several large birds (genus Gavia of the family Gaviidae) of Holarctic regions that feed on fish by diving and have their legs placed far back under the body for optimal locomotion underwater

Illustration of loon

Illustration of loon

Noun (2)

In the meaning defined above

Did you know?

There are a number of theories about the origin of loon as it refers to a crazy person, its most common current meaning. One is that it comes from loony, meaning "crazy." But based on currently available evidence, loony is a late 19th-century alteration of lunatic that didn't come into use until decades after the meaning of loon in question. (It's still possible that loony influenced the development and spread of this meaning of loon.) Another guess is that this loon is from the avian loon, inspired either by the bird's maniacal cry or its displays to distract predators, such as skittering over water with its neck crooked. This is certainly possible, and is the origin story favored by some. But the story our dictionaries favor is a bit more quotidian: the current use of loon developed from earlier uses, primarily in Scottish and other northern dialects of British English, of loon to refer to a lout (an awkward, brutish person) or idler (someone who is idle, lazy, or inactive). While that loon, which is from Middle English loun, never spread to British English more broadly, immigrants from the regions where it was used had a significant influence on American English, and it's not far-fetched to posit that their loon developed into the distinctly American use of the word to refer to daffy people.

First Known Use of loon

Noun (1)

15th century, in the meaning defined at sense 1

Noun (2)

1634, in the meaning defined above

History and Etymology for loon

Noun (1)

Middle English loun

Noun (2)

of Scandinavian origin; akin to Old Norse lōmr loon

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Time Traveler for loon

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The first known use of loon was in the 15th century

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Dictionary Entries Near loon

loom large



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Cite this Entry

“Loon.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/loon. Accessed 20 May. 2022.

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More Definitions for loon


\ ˈlün How to pronounce loon (audio) \

Kids Definition of loon

: a large diving bird that eats fish and has a black head and a black back spotted with white

More from Merriam-Webster on loon

Thesaurus: All synonyms and antonyms for loon

Nglish: Translation of loon for Spanish Speakers

Britannica.com: Encyclopedia article about loon


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