[doo-teer-ee-uhm, dyoo-]
noun Chemistry.
an isotope of hydrogen, having twice the mass of ordinary hydrogen; heavy hydrogen. Symbol: D; atomic weight: 2.01; atomic number: 1.

1933; < Greek deúter(os) second (see deutero-) + -ium Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
deuterium (djuːˈtɪərɪəm)
a stable isotope of hydrogen, occurring in natural hydrogen (156 parts per million) and in heavy water: used as a tracer in chemistry and biology. Symbol: D or ²H; atomic no: 1; atomic wt: 2.014; boiling pt: --249.7°C
[C20: New Latin; see deutero-, -ium; from the fact that it is the second heaviest hydrogen isotope]

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Word Origin & History

1933, coined by U.S. chemist Harold C. Urey, with Mod.L. ending, from Gk. deuterion, neut. of deuterios "having second place."
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

deuterium deu·te·ri·um (dōō-tēr'ē-əm, dyōō-)
An isotope of hydrogen with one proton and one neutron in the nucleus having an atomic weight of 2.014. Also called heavy hydrogen, hydrogen-2.

The American Heritage® Stedman's Medical Dictionary
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American Heritage
Science Dictionary
deuterium   (d-tîr'ē-əm)  Pronunciation Key 
An isotope of hydrogen whose nucleus has one proton and one neutron and whose atomic mass is 2. Deuterium is used widely as a tracer for analyzing chemical reactions, and it combines with oxygen to form heavy water. Also called heavy hydrogen. See Note at heavy water.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Britannica


isotope of hydrogen with atomic weight of approximately 2. Its nucleus, consisting of one proton and one neutron, has double the mass of the nucleus of ordinary hydrogen. Deuterium is a stable atomic species found in natural hydrogen compounds to the extent of 0.014 to 0.015 percent.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
Most current fusion efforts look to combine two atoms of deuterium, a heavier version of hydrogen with an extra neutron.
When a warhead detonates, it squeezes the deuterium and tritium until they fuse together.
What's more, so far they haven't included the deuterium and tritium fuel in the capsule for the tests.
The pusher-deuterium interface, which moved at the particle speed, was tracked to determine that speed.
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