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When saying the word for the SI/metric unit of long distances, the majority of the population pronounce "kilometre/kilometer" as "klomitr", akin to how words like " barometer " and "perimeter' are pronounced. How and why did this alternate pronunciation of " kilometer" come about?

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4 Answers 4

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In compound words derived from Greek, the linking vowel -o- is often stressed when followed by two syllables, the first of which ends with a vowel: consider astronomer/-my, astrologer/-gy, biographer/-phy, biology/-gist, cryptographer/-phy, geographer/-phy, geometer/-try, photographer/-phy, psychology/-gist.* This is a very general pattern, not confined to words for measuring instruments such as thermometer and odometer (although those probably exerted an especially strong analogical influence on the pronunciation of kilometre/kilometer).

The pronunciation kiˈlometer matches this common stress pattern, whereas the prescribed pronunciation ˈkiloˌmeter conflicts with this pattern.

The Oxford English Dictionary entry for kilometre notes that "The stress is marked by Webster (1828), Craig, and Cassell as kiˈlometre."

A related previous question is Pronunciation of tetrameter, pentameter, etc.


*In contrast, linking -o- is generally not stressed when it is followed by only one syllable, as in ˈastroˌnaut, ˈcryptoˌgram, ˈcryptoˌgraph, ˈpetroˌglyph, ˈphotoˌgraph, ˈpsychoˌpath. It also tends to be unstressed when followed by two syllables, the first of which ends in with a consonant, as in ˈgeoˌmancer/-cy, ˈgyroˌcopter, ˈnarcoˌlepsy, ˈnecroˌmancer/-cy,ˈorthoˌdoxy, ˈrhinoˌplasty.

Thus, in most words starting with kilo-, including kilogram and a number of others such as kilobar, kilobyte, kilogauss, kilohertz, kiloton(ne), kilovolt, kilowatt, there was no analogical support at all for putting the stress on the -o-, since it is only followed by one syllable in these words.

In theory, kilolitre/-liter would also meet the criteria I gave for stress on -o-: however, I don't know of any evidence that it has ever been pronounced with that stress pattern. The difference may be a result of kilolitre/-ter having a lower overall frequency and a lower frequency relative to its unprefixed counterpart than kilometre/-ter, as well as the lack of any preexisting common words ending in -ˈolitre or -ˈoliter.

Other prefixed forms of metre also seem not to show this stress pattern: aside from ˈdeciˌmetre, ˈcentiˌmetre, ˈmilliˌmetre (which use linking -i- rather than linking -o-, although the difference shouldn't necessarily be relevant), we find ˈnanoˌmetre, never (to my knowledge) *naˈnometre.

So it seems accurate to say that kiˈlometre/kiˈlometer stands out as an exception to the usual position of the stress in units with SI prefixes.

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    +1. The example of "gyrocopter" is interesting because the "copter" part is extracted from "helicopter" ("helico-" + "pter", meaning "helix wing"). Another complication is that the specific suffix sometimes matters: for example, words with "-ic" (or "-ical" or the like) are generally stressed on the last syllable before the "-ic", so they aren't stressed on the linking "-o-" even when they otherwise meet the criteria you mention: hence "ge'ology" but "geo'logic (time)", "pho'tography" but "photo'graphic", etc.
    – ruakh
    Commented Jun 25 at 17:26
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    For what it's worth, in Modern Greek—whose pronunciation bears little if any similarity to that of Ancient Greek—we pronounce kilometer (χιλιόμετρο) with the emphasis on the o, pretty close to the pronunciation in English. If that was also the case in Ancient Greek, it might have affected the pronunciation in English. Maybe? The other examples in your first paragraph, or at least their modern Greek equivalents, have the emphasis on the third or later syllables instead.
    – terdon
    Commented Jun 26 at 17:33
  • I use kilo'meter. Like deve'lopment.
    – Lambie
    Commented Jun 27 at 13:39
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It is very probably deemed to be "incorrect" in view of the pronunciation of "millimeter", "centimeter", "kilogram", "milligram", "kilohertz", etc.; in the light of the evident pattern that shows in these words it is certainly an anomalous pronunciation. Until recently the pronunciation of "kilometer" in BrE was as expected (/ˈkɪl.əˌmiːt ə/) (LPD, 2000 edition); the dominant pronunciation is now /kɪˈlɒm.ɪt ə/ (LPD, 2008 edition, 63% now), where stress is as in AmE (/kɪˈlɑː.mə.t̬ɚ/). It is to be suspected that the influence of AmE is at the root of this change. The pronunciation of "millimeter", centimeter", etc. has not changed in AmE.

LPD 2000 —On the analogy of 'centimeter, 'millimeter, it is clear that the stressing 'kilometer is logical and might be expected to predominate.
Nevertheless, many people (particularly in the US, but also elsewhere) say kiˈlom-. Poll panel preferences: BrE 1988, ˈkɪl- 52%, ˈlɒm- 48%; AmE 1993, ˈlɑːm-, 84%, ˈkɪl 16%, BrE 1998, ˈlɒm- 57%, ˈkɪl- 43%.

LPD: Longman Pronunciation Dictionary

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    OED notes parenthetically: “(The stress is marked by Webster (1828), Craig, and Cassell as kiˈlometre.)”
    – tchrist
    Commented Jun 24 at 0:04
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    Worth noting that although the USA uses imperial units for distance in general, the military, engineering, and other technical industries use metric, so kilometer is more common in AmE than one would naively expect.
    – Dale M
    Commented Jun 24 at 6:17
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    I associate the pronunciation with the stress on the first syllable very strongly with Canada. It seems that it was specifically and explicitly decided that the pronunciation should match other units of measure (centimeter, etc.) rather than devices (speedometer, etc.). I didn't ask about spelling, where at least in Britain "metre" is a unit and "meter" is a device; Canadian spelling is often somewhere in between.
    – phoog
    Commented Jun 24 at 6:48
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    @DaleM - So does the UK! We mainly talk about kilometres in the context of travelling in mainland Europe. Commented Jun 24 at 7:36
  • On forvo, the pronunciation is with tonic stress on lo in UK English: forvo.com/search/kilometer/en_uk And that's how I say it.
    – Lambie
    Commented Jun 25 at 13:59
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There are a lot of words with the suffix "-ometer". Many are quite specialised! I can appreciate that distinguishing among them would be made easier if the part before '...ometer' is emphasised. This is perhaps the OP's reason for asserting a 'right' and 'wrong' pronounciation. Nevertheless, for reasons I can't explain, my instinctive default with most of these words (a selection shown below) is to put a primary stress on the 'O' of '...ometer'. In fact, on reflection, I'd say that some SI units - n'anometer, k'ilometer - are exceptions to the rule.

odometer

geometer

barometer

kilometer

pedometer

pyrometer

optometer

vinometer

taxometer

cryometer

atmometer

gasometer

gyrometer

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    But "kilometer" doesn't have the "-ometer" suffix (meaning "measuring device"); instead it's "kilo + meter." Though you're probably right that this pattern in other words ending in "ometer" has caused the odd pronunciation of "kilometer" also.
    – alphabet
    Commented Jun 23 at 22:30
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    Indeed. Possibly a case of rebracketing. I suspect you're right that "nanometer" hasn't been affected because it's used less often.
    – alphabet
    Commented Jun 23 at 22:37
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    @alphabet - yes, 'rebracketing' seems like it's 'the answer'. Post that as an answer for a +1 from me!
    – Dan
    Commented Jun 23 at 22:42
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    @Dan because there more non-scientists than scientists! 😀
    – justhalf
    Commented Jun 24 at 8:07
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    @Dan By the same token, doesn't a kilogram sound like a particularly cheerful contract assassination? (Singing and balloons optional.)
    – FeRD
    Commented Jun 24 at 12:04
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The word first appeared in French in 1795

OED

A borrowing from French.

Etymon: French kilomètre.

From French kilomètre (1795): see kilo- comb. form and metre n.2 (The stress is marked by Webster (1828), Craig, and Cassell as kiˈlometre.)

Background from Wikipedia:

Charles Maurice de Talleyrand championed a new system based on natural units, proposing to the French National Assembly in 1790 that such a system be developed. The Assembly defined the 'metre' and its length as one ten-millionth of the length of an Earth quadrant, the length of the meridian arc on the Earth's surface from the equator to the north pole. In 1799, after the arc measurement had been surveyed, the new system was launched in France.

The French had hopes of interesting Britain in the new system but their offer was ignored.

The first written example of “Kilometre” in English was in 1810: “Killometer, 1000 M. Naval Chronicle vol. 24 301", which may or may not give some clue as to its pronunciation as it does not appear to be the same as Webster, Craig, and Cassel above, or the OED below:

The OED gives

British English /ˈkɪləˌmiːtə/ and /kᵻˈlɒmᵻtə/ and American English /kᵻˈlɑmədər/ and /ˈkɪləˌmidər/

Early attempts at pronunciation are based upon four approaches:

  1. A knowledge of French, hearing the word in French and taking the French pronunciation

  2. Hearing someone who has a knowledge of French say the word and then attempting repetition.

  3. Reading the word and, with a knowledge of French, attempting a pronunciation.

  4. Reading the word and, with or without a knowledge of French, attributing an anglicised pronunciation.

  5. Later, i.e. current, pronunciation is based chiefly upon the speaker's first hearing the word. This may be modified by future experience.

Where did the pronunciation of the word "kilometer/kilometre" as "kl OM iter" rather than "KILL o meeter" originate?.

This then seems to fall into 5. above, which, in its turn is modified by 4.

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