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mass communication
mass defect
mass-energy equation
mass-energy equivalence
mass extinction
mass-market
mass media
mass noun
mass number
mass observation
mass-produce
mass production
mass society
mass sociogenic illness
mass spectrometer
mass spectrum
mass transit
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mass number
mass num·ber (plural mass num·bers)


noun 
Definition:
 
number of protons and neutrons: the number of protons and neutrons in the nucleus of an atom of a particular substance.
Symbol  A
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