atomic mass vs atomic weight

atomic mass and atomic weight both are nouns.

Word	Noun	Adjective	Verb	Adverb
atomic mass	Yes	No	No	No
atomic weight	Yes	No	No	No

As nouns, atomic mass and atomic weight are synonyms defined as:

atomic mass and atomic weight: (chemistry) the mass of an atom of a chemical element expressed in atomic mass units

Other synonyms of atomic mass include relative atomic mass.

atomic mass (noun)	atomic weight (noun)
(chemistry) the mass of an atom of a chemical element expressed in atomic mass units	(chemistry) the mass of an atom of a chemical element expressed in atomic mass units