kilometer

Etymology

It is borrowed from French kilomètre,^{[2][3][4][5][6]} coined in French in 1795,^[2][3] when the metric system was officially adopted in France,^[3] from kilo- (“thousand”) and mètre (“metre”).^[3][4][7] The prefix is an arbitrary shortening of Ancient Greek χίλιοι (khílioi, “a thousand”);^[3][2] the OED explains that the French reformers transcribed the Greek word with k rather than ch and chose the form kilo- for a clear pronunciation, for euphony and to avoid homophones.^[8] The second part, mètre, is from μέτρον (métron, “measure”).^[7] The spelling kilometre is chiefly British.^[2][6]

Earliest recorded meaning

A unit of length of one thousand metres: Etymonline finds it by 1799 in translations from French.^[2] The 1989 edition of the OED, Barnhart and Merriam-Webster give 1810,^[9][3][4] and Dictionary.com 1800–10.^[6]

Semantic evolution

The word has kept its single meaning, a metric measure of length equal to a thousand metres, or about five-eighths of a mile.^[9][5][10] Its pronunciation has changed more: stress on the first syllable, as in centimetre and millimetre, has been used since the early 1800s, while stress on the second syllable was first recorded in America before 1830 and is now the more common in North America and frequent in Britain.^[6][4] From 1828 to 1841 Noah Webster gave only the second-syllable stress.^[4]

Timeline

• 1799 – in English, in translations from French.^[2] The 1989 edition of the OED and Merriam-Webster date it to 1810.^[9][4]
• before 1830 – the pronunciation with stress on the second syllable is first recorded, in America.^[6]

Meanings

Noun

1. A metric unit of length equal to 1,000 meters, about 0.62 of a mile; abbreviated km: The village is three kilometers from the coast.^[10][4][5]

Word family

• kilometric
• square kilometer

Related words

• meter
• kilogram
• kilo
• chiliad
• metric

Usage notes

Both pronunciations, with stress on the first or the second syllable, are used by educated speakers.^[6] Critics of the second-syllable stress argue from the pattern of centimeter and millimeter,^[4][6] but it is supported by the stress of instrument names such as thermometer and barometer.^[6] Merriam-Webster notes that kilometer does not in fact follow the other metric compounds.^[4]

References

1. ^ a b Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
3. ^ a b c d e f Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
4. ^ a b c d e f g h i Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
5. ^ a b c Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
6. ^ a b c d e f g h Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
7. ^ a b Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
8. ^ Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
9. ^ a b c Simpson, J. A.; Weiner, E. S. C., eds. (1989), The Oxford English Dictionary, 2nd ed., Oxford: Clarendon Press
10. ^ a b The American Heritage Dictionary of the English Language (1992), 3rd ed., Boston: Houghton Mifflin