Dictionary

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

First Known Use of MASS NUMBER

1923

mass number

noun    (Medical Dictionary)

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

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