[proh-tee-uhm, -shee-uhm]
noun Chemistry.
the lightest and most common isotope of hydrogen. Symbol: H 1

1930–35; prot- + -ium Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
protium (ˈprəʊtɪəm)
the most common isotope of hydrogen, having a mass number of 1
[C20: New Latin, from proto- + -ium]

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Medical Dictionary

protium pro·ti·um (prō'tē-əm, prō'shē-)
See hydrogen-1.

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
protium   (prō'tē-əm, -shē-əm)  Pronunciation Key 
The most abundant isotope of hydrogen, having an atomic mass of 1. Its nucleus consists of a single proton. See more at hydrogen.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Britannica


isotope of hydrogen (q.v.) with atomic weight of approximately 1; its nucleus consists of only one proton. Ordinary hydrogen is made up almost entirely of protium.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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