atomic mass

[ uh-tom-ik mas ]

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.

atomic mass

noun

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

atomic mass

1. The mass of a given atom or molecule, expressed in atomic mass units.
2. Compare atomic weightSee also mass number

Word History and Origins

Origin of atomic mass¹

First recorded in 1895–1900