atomic masses

noun Chemistry.

the mass of an isotope of an element measured in units formerly based on the mass of one hydrogen atom taken as a unit or on ¹ / ₁₆ the mass of one oxygen atom, but after 1961 based on ¹ / ₁₂ the mass of the carbon-12 atom. Abbreviation: at. m.

Origin:
1895–1900

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Based on the Random House Dictionary, © Random House, Inc. 2013.
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World English Dictionary

atomic mass

—n
1.	the mass of an isotope of an element in atomic mass units
2.	short for relative atomic mass See atomic weight

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Atomic masses is always a great word to know.

So is callithumpian. Does it mean:

a children's mummer's parade, as on the Fourth of July, with prizes for the best costumes.

a calculus or concretion found in the stomach or intestines of certain animals, esp. ruminants, formerly reputed to be an effective remedy for poison.

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American Heritage

Medical Dictionary

atomic mass n.
The mass of an atom, usually expressed in atomic mass units.

American Heritage

Science Dictionary

atomic mass
The mass of a given atom or molecule, expressed in atomic mass units. Compare atomic weight. See also mass number.

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"When you see something that is technically sweet, you go ahead and do it and you argue about what to do about it only after you have had your technical success. That is the way it was with the atomic bomb."

-J. Robert Oppenheimer

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