atomic mass

noun, Chemistry
1.
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 (0.0625) the mass of one oxygen atom, but after 1961 based on 1/12 (0.0833) the mass of the carbon-12 atom.
Abbreviation: at. m.
Origin
1895-1900
British Dictionary definitions for atomic mass

atomic mass

noun (chem)
1.
the mass of an isotope of an element in atomic mass units
2.
short for relative atomic mass See atomic weight
atomic mass in Medicine

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

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

the quantity of matter contained in an atom of an element. It is expressed as a multiple of one-twelfth the mass of the carbon-12 atom, 1.992646481023gram, which is assigned an atomic mass of 12 units. In this scale 1 atomic mass unit (amu) corresponds to 1.660538731024gram.

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