• synonyms


  1. Meteorology. a line on a weather map or chart connecting points having equal temperature.
  2. Also called isothermal line. Physics. a curve on which every point represents the same temperature.
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Origin of isotherm

First recorded in 1855–60; back formation from isothermal
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for isotherm

Historical Examples of isotherm

  • This is shown by the isotherm for -4.5, which surrounds the point Q, the melting point of the ternary salt.

    The Phase Rule and Its Applications

    Alexander Findlay

  • The scale must, however, be laid perpendicularly to the isotherm, as before.

  • Isotherm, a compound of two Greek words meaning equal temperature, is the name given in meteorology to such lines as this.

  • Draw an isotherm east and west across the map, through your station.

  • On a second blank weather map draw an isotherm through your station inclined from northwest to southeast.

British Dictionary definitions for isotherm


  1. a line on a map linking places of equal temperature
  2. physics a curve on a graph that connects points of equal temperature
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Also called: isothermal, isothermal line
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 isotherm


1860, from French isotherme (Humboldt, 1817), from Greek iso- (see iso-) + therme "heat" (see thermal).

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Online Etymology Dictionary, © 2010 Douglas Harper

isotherm in Science


  1. A line drawn on a weather map connecting points that have the same temperature. Each point can mark one temperature reading or an average of several readings.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.