Meteorology. a line drawn on a weather map or chart that connects points at which the barometric pressure is the same.
Also, isobare [ahy-suh-bair] . Physics, Chemistry. one of two or more atoms having equal atomic weights but different atomic numbers.
Compare isotope.

1860–65; < Greek isobarḗs of equal weight. See iso-, baro-

isobarism, noun Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
isobar (ˈaɪsəʊˌbɑː)
1.  a line on a map connecting places of equal atmospheric pressure, usually reduced to sea level for purposes of comparison, at a given time or period
2.  physics Compare isotope any of two or more atoms that have the same mass number but different atomic numbers: tin-115 and indium-115 are isobars
[C19: from Greek isobarēs of equal weight, from iso- + baros weight]

Collins English Dictionary - Complete & Unabridged 10th Edition
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Word Origin & History

1864, coined from Gk. isos "equal," + baros "weight," from barys "heavy" (see grave (adj.)).
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

isobar i·so·bar (ī'sə-bär')

  1. Any of two or more kinds of atoms having the same atomic mass but different atomic numbers.

  2. A line on a weather map connecting points of equal atmospheric pressure.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
isobar   (ī'sə-bär')  Pronunciation Key 
A line drawn on a weather map connecting places having the same atmospheric pressure. The distance between isobars indicates the barometric gradient (the degree of change in atmospheric pressure) across the region shown on the map. When the lines are close together, a strong pressure gradient is indicated, creating conditions for strong winds. When the lines are far apart, a weak pressure gradient is indicated and calm weather is forecast.
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Encyclopedia Britannica


line on a weather map of constant barometric pressure drawn on a given reference surface. The isobaric pattern on a constant-height surface is extremely useful in weather forecasting because of the close association between pressure and weather. Regions of low pressure at sea level tend to be areas of bad weather, especially in winter. At higher elevations the wind blows approximately parallel to the isobars, with low pressure to the left in the Northern Hemisphere and to the right in the Southern Hemisphere with respect to the direction of air movement; the closer together the isobars are, the stronger is the wind speed. Only sea-level pressure patterns are routinely used in meteorology. At higher elevations pressure itself is used to define the reference surface upon which contours of the height above sea level are drawn; dynamically, the height contours of a constant pressure surface are completely analogous to the isobars of a constant-height surface

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
We describe and apply the isobar-hole approach to intermediate energy pion-nucleus reactions.
Therefore, areas of cross-isobar flow are also representative of thermal advection.
Special flag for estimated radius of outermost closed isobar.
Then continue with the remaining values until you have all the reports connected with an isobar.
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