noun, plural lo·cos.

Slang. an insane person; maniac.
Veterinary Pathology. locoism.

verb (used with object), lo·coed, lo·co·ing.

to poison with locoweed.
Slang. to cause to be insane or crazy.


Slang. out of one's mind; insane; crazy.

Origin of loco

1835–45, Americanism; < Spanish: insane

in loco

[in loh-koh]

adverb Latin.

in place; in the proper place.

Origin of in loco

First recorded in 1700–10

in loco parentis

[in loh-koh pah-ren-tees; English in loh-koh puh-ren-tis]

adverb Latin.

in the place or role of a parent.

loco citato

[loh-koh ki-tah-toh; English loh-koh sahy-tey-toh, si-tah-toh]

adverb Latin.

loco primo citato

[loh-koh pree-moh ki-tah-toh; English loh-koh prahy-moh sahy-tey-toh, pree-moh si-tah-toh]

adverb Latin.

loco supra citato

[loh-koh soo-prah ki-tah-toh; English loh-koh soo-pruh sahy-tey-toh, si-tah-toh]

adverb Latin.

suo loco

[soo-oh law-koh; English soo-oh loh-koh]

adverb Latin.

in one's own or rightful place.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for loco

Contemporary Examples of loco

Historical Examples of loco

British Dictionary definitions for loco




informal short for locomotive




slang, mainly US insane
(of an animal) affected with loco disease

noun plural -cos

short for locoweed

verb (tr)

to poison with locoweed
US slang to make insane

Word Origin for loco

C19: via Mexican Spanish from Spanish: crazy




denoting a price for goods, esp goods to be exported, that are in a place specified or known, the buyer being responsible for all transport charges from that placeloco Bristol; a loco price

Word Origin for loco

C20: from Latin locō from a place

in loco parentis

in place of a parent: said of a person acting in a parental capacity

loco citato

in the place or passage quotedAbbreviation: loc. cit, lc

Word Origin for loco citato

Latin: in the place cited

suo loco


mainly law in a person or thing's own or rightful place

Word Origin for suo loco

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for loco

1844, American English, from Spanish loco (adj.) "insane," of uncertain origin, perhaps from Arabic lauqa, fem. of 'alwaq "fool, crazy person." Loco-weed (1877) was name given to species of western U.S. plants that cause cattle and horse diseases that make them stagger and act strangely.

in loco parentis

Latin, literally "in the place of a parent" (see parent).

Online Etymology Dictionary, © 2010 Douglas Harper

Culture definitions for loco

in loco parentis

[(in loh-koh puh-ren-tis)]

To assume the duties and responsibilities of a parent: “Because Jack's parents were out of town, his sister acted in loco parentis and punished him for staying out so late.” From Latin, meaning “in the place of a parent.”


At one time, colleges and universities acted in loco parentis for their students, but this is no longer true.
The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.