atomic mass

Use the noun atomic mass when you're talking about the mass of an atom's protons, neutrons, and electrons.

You'll come across the term atomic mass if you study chemistry, in which it refers to a single atom of some chemical and the total mass of that atom. The unit of measurement is an "atomic mass unit" or amu. Mass is a measurement in science which is essentially the same as weight, without taking changes in gravity into account, and atomic means "of an atom." The two were first combined into atomic mass in the mid-1800s.

Definitions of atomic mass
  1. noun
    (chemistry) the mass of an atom of a chemical element expressed in atomic mass units
    synonyms: atomic weight, relative atomic mass
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    types:
    combining weight, eq, equivalent, equivalent weight
    the atomic weight of an element that has the same combining capacity as a given weight of another element; the standard is 8 for oxygen
    meq, milliequivalent
    one-thousandth of an equivalent
    type of:
    mass
    the property of a body that causes it to have weight in a gravitational field
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