adjective
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slang insane
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(of an animal) affected with loco disease
noun
verb
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to poison with locoweed
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slang to make insane
noun
adjective
Etymology
Origin of loco
1835–45, < Spanish: insane
Explanation
If someone calls you loco, it means they think you're nutty or eccentric. Your friends will think your dog is completely loco if she spends hours every day chasing her own tail. You can use the slang term loco when you're commenting on the craziness or irrationality of a person or situation. You might say, for example: "This meeting is totally loco — everyone's talking at the same time!" Loco comes from American English, which borrowed it from the Spanish loco, "insane." Its roots are uncertain, but it may stem from the Arabic lauqa, "fool."
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Coaches often serve in loco parentis, guiding a developing prospect not only through training and tournaments but also the awkward riddles of growing up.
From The Wall Street Journal • Dec. 23, 2025
"The loco pilot, on observing the herd of elephants, applied emergency brakes. However, elephants dashed with the train," he said.
From Barron's • Dec. 20, 2025
It’s been bien loco, like I say in the song.
From Los Angeles Times • Sep. 4, 2025
On the return journey, a bolt sheared on what is now more widely known as the Penydarren loco, causing the boiler to leak.
From BBC • Feb. 24, 2024
“So your pelo loco, like clippings of grass, will not disarrange this house,” she says.
From "Beast Rider" by Tony Johnston & María Elena Fontanot de Rhoads
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
