gram atom vs weight unit

gram atom and weight unit both are nouns.

Word	Noun	Adjective	Verb	Adverb
gram atom	Yes	No	No	No
weight unit	Yes	No	No	No

As nouns, weight unit is a hypernym of gram atom; that is, weight unit is a word with a broader meaning than gram atom:

gram atom: the quantity of an element whose weight in grams is numerically equal to the atomic weight of the element
weight unit: a decimal unit of weight based on the gram

Other hypernyms of gram atom include metric weight unit.

gram atom (noun)	weight unit (noun)
the quantity of an element whose weight in grams is numerically equal to the atomic weight of the element	a unit used to measure weight
	a decimal unit of weight based on the gram