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loco

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Etymology and origin of the English word loco

Pronunciation

  • UK: /ˈləʊ.kəʊ/[1]

loco1 musical direction, in the written register

Confidence
Established
Formation
Borrowing
First attested
1786 Busby, Complete Dictionary of Music
Borrowed from
Italian loco
Ultimate origin
Latin locus

Etymology

The musical direction is borrowed from Italian loco (“place”),[2][3][4] from Latin locō, the ablative of locus (“place”).[2][3] Merriam-Webster's Collegiate explains it as dialectal Italian for "there", from in locō (“in the place”),[5] and Merriam-Webster Unabridged as short for al loco, literally "at the passage";[4] the OED notes that this fuller form does not seem to follow Italian usage.[2]

Earliest recorded meaning

Back at the written pitch after a passage played an octave higher or lower: 1786, in Thomas Busby's Complete Dictionary of Music.[2] Merriam-Webster dates it to about 1801.[4]

Timeline

  • 1786 – in music, a return to the written pitch.[2] Merriam-Webster dates it to about 1801.[4]

Meanings

Adverb

  1. (music) At the written pitch, after a passage marked to be played an octave higher or lower; in string playing, with the left hand back in its normal position.[4][2][3]

loco2 crazy; locoweed

Confidence
Established
Formation
Borrowing
First attested
1844 St Louis Reveille
Borrowed from
Spanish loco

Etymology

The word for crazy is borrowed from Spanish loco (“mad, insane, crazy”),[2][6][7][4][3] which Merriam-Webster and Collins take into English through Mexican Spanish.[4][8] The Spanish adjective is recorded from the 13th century and implied earlier by locura (“madness”) (12th century), and it is related to Portuguese louco in the same sense; its further origin is uncertain and disputed.[2] The American Heritage Dictionary, Barnhart and Etymonline suggest that it may come from the feminine of an Arabic adjective meaning foolish, a word for a fool,[3][7][6] while Partridge took the Spanish and Portuguese words to be of Araucanian origin.[9] The plant name is probably shortened from American Spanish yerba loca or hierba loca (18th century), "mad plant", from yerba (“plant”) and loca, the feminine of loco, for its effect on livestock; the ending was probably changed after the masculine form.[2]

Earliest recorded meaning

Any of several plants of the American West and Southwest that poison livestock, now usually locoweed: 1844, in the St Louis Reveille.[2][7][4] Etymonline dates the adjective "crazy" to the same year and thinks it the older word.[6]

Semantic evolution

The OED and Etymonline record the adjective from 1852 and 1844, Barnhart, Merriam-Webster and the Dictionary of American Regional English only from 1887, when a Western speaker in Outing said horses would "go plumb loco".[2][6][7][4][10][11] Loco was also the disease that the plants cause in livestock (1876)[2][10] and a crazy person (1852).[11][4] The verb, to poison with locoweed, is recorded from 1884;[4][10] an 1887 article in Scribner's Magazine, quoted by the Dictionary of American Regional English, explains that a verb sprang from the noun, that cattle showing signs of madness were said to be locoed, and that the word was finally extended to human beings.[10] From 1897 the verb also meant to drive someone mad.[11][4] The adjective was at first chiefly Western, but has spread more widely.[10]

Timeline

  • 1844 – the plant, locoweed.[2][7][4] Etymonline dates the adjective to the same year.[6]
  • 1852 – adjective, crazy, wild, irrational.[2] Barnhart and Merriam-Webster date it to 1887.[7][4]
  • 1852 – noun, a crazy person.[11]
  • 1876 – loco disease, the disease of livestock caused by the plant.[2]
  • 1884 – verb, to poison with locoweed.[4][10]
  • 1897 – verb, to drive mad.[11]

Meanings

Adjective

  1. (slang, chiefly US) Crazy, out of one's mind; often go loco: The crowd went loco when the band came on.[8][4][2]
  2. Of an animal, suffering from loco disease.[8][10]

Noun

  1. Locoweed.[8][4][2]
  2. Loco disease, a disease of livestock caused by eating locoweed.[4][2][10]
  3. (slang) A crazy person.[4][11]

Verb

  1. To poison an animal with locoweed.[8][4][10]
  2. (US slang) To make someone crazy.[8][4][11]

Word family

  • locoweed
  • locoism
  • locoed

Usage notes

Loco is also a short form of locomotive, recorded from 1833,[2][8][12] and in 19th-century American politics was short for locofoco, a Democrat.[2][12][4]

References

  1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
  2. ^ a b c d e f g h i j k l m n o p q r s t Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
  3. ^ a b c d e The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt
  4. ^ a b c d e f g h i j k l m n o p q r s t u v Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
  5. ^ Merriam-Webster's Collegiate Dictionary (2003), 11th ed., Springfield, Mass.: Merriam-Webster
  6. ^ a b c d e Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
  7. ^ a b c d e f Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
  8. ^ a b c d e f g Collins English Dictionary (2023), Glasgow: HarperCollins
  9. ^ Partridge, Eric (1966), Origins: A Short Etymological Dictionary of Modern English, 4th ed., London: Routledge & Kegan Paul
  10. ^ a b c d e f g h i Cassidy, Frederic G. & Joan Houston Hall (eds.) (1985–2002), Dictionary of American Regional English, vols I–IV, Cambridge, Mass.: Belknap Press of Harvard University Press
  11. ^ a b c d e f g Green, Jonathon (2010), Green's Dictionary of Slang, London: Chambers; digital ed. 2016–, https://greensdictofslang.com
  12. ^ a b Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press

Related etymologies

Cite this entry

“Loco.” Etymologically, 1 Nov. 2026, etymologically.com/en/loco. Accessed 1 Nov. 2026.

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