mass number

noun

Definition of mass number

: an integer that approximates the mass of an isotope and designates the number of nucleons in the nucleus

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An initial look at comments supporting the blackout repeal didn’t indicate similar issues with fake names or mass numbers of identical letters. — Paul Overberg, WSJ, "The NFL’s Other Problem: Fake Fans Lobbying for the Blackout," 7 Sep. 2018

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mass of the catechumens

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The first known use of mass number was in 1923

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mass number

noun

Medical Definition of mass number

: an integer that approximates the mass of an isotope and that designates the number of nucleons in the nucleus the symbol for carbon of mass number 14 is ¹⁴C or C¹⁴ — compare atomic mass