from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun An instrument for measuring temperature, especially one having a graduated glass tube with a bulb containing a liquid, typically mercury or colored alcohol, that expands and rises in the tube as the temperature increases.

from The Century Dictionary.

  • noun An instrument by which the temperatures (see temperature and thermometry) of bodies are ascertained, founded on the common property belonging to all bodies, with very few exceptions, of expanding with heat, the rate or quantity of expansion being supposed to be proportional to the degree of heat applied, and hence indicating that degree.
  • noun Hence, figuratively, anything which (roughly) indicates temperature.
  • noun A thermometer whose action is based on the variation of electrical resistance produced by changes of temperature in a metallic conductor. The difference in the resistance between a current passing through a conductor of known and one of unknown temperature gives the difference of temperature between the two. Also called differential-resistance thermometer. The most delicate form in which the principle is applied is the bolometer.
  • noun The Rutherford maximum has a light movable steel index at the top of the mercurial column. The tube is placed horizontal, and as the temperature rises the mercury pushes the index before it. When the temperature falls, the index is left in situ to mark the position of the maximum.
  • noun In Phillips's maximum, a small bubble of air makes a break in the upper part of the mercurial column. When the temperature begins to fall, the detached portion of the column is left behind to register the highest temperature.
  • noun The Negretti maximum has the bore of the tube partly closed by a constriction just above the bulb. In rising temperatures mercury is forced from the bulb past the constriction, but when the temperature falls the mercury cannot readily return to the bulb, and the top of the mercurial column indicates the maximum temperature. In order to reset the thermometer to the current air-temperature, the mercury is forced back into the bulb by whirling the instrument on a swing-pin. This form of maximum is used at the stations of the United states Weather Bureau.

from the GNU version of the Collaborative International Dictionary of English.

  • noun (Physics) An instrument for measuring temperature, founded on the principle that changes of temperature in bodies are accompanied by proportional changes in their volumes or dimensions.
  • noun etc. See under Air, Balance, etc.
  • noun a form of thermometer indicating changes of temperature by the expansion or contraction of rods or strips of metal.
  • noun a thermometer that registers the maximum and minimum of temperature occurring in the interval of time between two consecutive settings of the instrument. A common form contains a bit of steel wire to be pushed before the column and left at the point of maximum temperature, or a slide of enamel, which is drawn back by the liquid, and left within it at the point of minimum temperature.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun An apparatus used to measure temperature.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • noun measuring instrument for measuring temperature


from Wiktionary, Creative Commons Attribution/Share-Alike License

From French thermomètre.


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  • A question for all you British spellers in the Wordieverse. Why isn't this word spelled *thermometre? Like metre, kilometre, etc. (I would assume the same "American" spelling goes for other measuring devices with names ending in -meter.)

    Qroqqa? Anyone?

    July 2, 2009

  • I assume it's by analogy with the way we form subject-nouns from verbs. Someone who thinks is a thinker, someone who measures is a measurer. Similarly for inanimate objects - the thing that stops up your drain is a stopper. Thus, the "er" ending seems more appropriate for a thermometer, or any other measuring device.

    July 2, 2009

  • So you're saying that a thermometer is a device that thermomets (or thermometes)?

    July 2, 2009

  • The units of measurement metre, litre are comparatively recent borrowings from French and for a long time the metric system was written exactly in French fashion (mètre, kilogramme) because it was only in foreign use.

    The real comparison is with longer-established words such as centre, theatre, and metre "rhythm". These are the natural developments of French words from Latin and ultimately from Greek. The development was with vowel weakening to give centrum > *centro > centre (with change of k to s in there too). So this spelling and the corresponding pronunciations in French and English are regular.

    However, metre "rhythm" had the spelling meter in OE, perhaps influenced by the native elements mete "measure" + agent suffix. The fact that the Modern English -er and -re are pronounced the same could not have operated then. In French there was a final schwa, and this would have been retained in borrowings into English. I think what happened to make the two endings alike is that when final schwa was lost in English, sentrə giving sentr, an epenthetic schwa was then inserted to avoid this awkward final cluster, giving sentər.

    Entirely the same thing should have happened from start to finish with the compound devices such as thermometer, had such things existed in ancient times. They too should have been neuters ending in -trum, the Latin equivalent of the Greek -tron. But instead they occurred as words of the ager ~ agris type where there is an endingless nominative with an epenthetic vowel: thus nom. altimeter, acc. altimetrum. (This is the word the OED thinks might have been the origin of the French suffix; it was a post-classical Latin word, compounded of Latin first half with the Greek suffix. So the tradition of creating hybrids like speedometer goes way back.)

    The model for Latin words like altimeter is the classical metrical terms such as hexameter, which were actually adjectives, so the -er ending was more convenient or more normal rather than borrowing them as -rus, -ra, -rum types. I'm not sure why.

    Modern scientific words are borrowed from the Latin citation form, the nominative, so we create thermometer. Historically however the nominative died out and the accusative survived through Romance into Middle French. If these had been everyday words they would also have gone from *-metrum to **-metre.

    July 2, 2009

  • Looks like qroqqa has slam dunked the etymological story.

    Beyond that, the situation with regards to current usage in clear in my mind. metre is used with actual units of measurement, e.g. nanometre, centimetre, etc. meter is used with instruments of measurement, e.g. thermometer, site-meter, etc. I think it's a useful distinction regardless of how it came about.

    July 2, 2009

  • Thanks, Q! That was excellent!

    July 3, 2009