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[ahy-suh-tohp] /ˈaɪ səˌtoʊp/
noun, Chemistry.
any of two or more forms of a chemical element, having the same number of protons in the nucleus, or the same atomic number, but having different numbers of neutrons in the nucleus, or different atomic weights. There are 275 isotopes of the 81 stable elements, in addition to over 800 radioactive isotopes, and every element has known isotopic forms. Isotopes of a single element possess almost identical properties.
Origin of isotope
1910-15; iso- + -tope < Greek tópos place
Related forms
[ahy-suh-top-ik] /ˌaɪ səˈtɒp ɪk/ (Show IPA),
isotopically, adverb Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2016.
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Examples from the Web for isotope
Contemporary Examples
Historical Examples
  • Why nail the "power metal" down to an isotope of gold with an atomic weight of 197?

    Despoilers of the Golden Empire Gordon Randall Garrett
  • An isotope is just a different variety of the ordinary kind of atom in each element.

    The Caves of Fear John Blaine
  • There must be another one in either wing, for the isotope plant and the cartridge-case plant.

    The Cosmic Computer Henry Beam Piper
  • Well, heavy water is made of one atom of oxygen plus two atoms of deuterium, which is the first isotope of hydrogen.

    The Caves of Fear John Blaine
British Dictionary definitions for isotope


one of two or more atoms with the same atomic number that contain different numbers of neutrons
Derived Forms
isotopic (ˌaɪsəˈtɒpɪk) adjective
isotopically, adverb
isotopy (aɪˈsɒtəpɪ) noun
Word Origin
C20: from iso- + Greek topos place
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
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Word Origin and History for isotope

1913, literally "having the same place," introduced by British chemist Frederick Soddy (1877-1956) on suggestion of Margaret Todd, from Greek isos "equal" (see iso-) + topos "place" (see topos); so called because despite the different atomic weights, the various forms of an element occupy the same place on the periodic table.

Online Etymology Dictionary, © 2010 Douglas Harper
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isotope in Medicine

isotope i·so·tope (ī'sə-tōp')
One of two or more atoms having the same atomic number but different mass numbers.

i'so·top'ic (-tŏp'ĭk) adj.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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isotope in Science
One of two or more atoms that have the same atomic number (the same number of protons) but a different number of neutrons. Carbon 12, the most common form of carbon, has six protons and six neutrons, whereas carbon 14 has six protons and eight neutrons. Isotopes of a given element typically behave alike chemically. With the exception of hydrogen, elements found on Earth generally have the same number of protons and neutrons; heavier and lighter isotopes (with more or fewer neutrons) are often unstable and undergo radioactive decay.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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isotope in Culture
isotope [(eye-suh-tohp)]

In physics, different forms of the same element, with nuclei that have the same number of protons but different numbers of neutrons. Isotopes are distinguished from each other by giving the combined number of protons and neutrons in the nucleus. For example, uranium 235 is the isotope of uranium that has 235 protons and neutrons in its nucleus rather than the more commonly occurring 238. All elements have isotopes.

The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Slang definitions & phrases for isotope

in the trenches

adverb phrase

In the workplace; in contact with the people or problems in a situation; unprotected by distance or illusion: I needed to be back in the trenches where I could really relate to a community/More retrospective accounts are elegant and noble. Watson told it like it was in the trenches (1970s+)

The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D.
Copyright (C) 2007 by HarperCollins Publishers.
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