buxomness vs plumpness

buxomness and plumpness both are nouns.

Word	Noun	Adjective	Verb	Adverb
buxomness	Yes	No	No	No
plumpness	Yes	No	No	No

As nouns, plumpness is a hypernym of buxomness; that is, plumpness is a word with a broader meaning than buxomness:

buxomness: the bodily property of being attractively plump and vigorous and (of women) full-bosomed
plumpness: the bodily property of being well rounded

Other hypernyms of buxomness include embonpoint, roundness.

buxomness (noun)	plumpness (noun)
the bodily property of being attractively plump and vigorous and (of women) full-bosomed	the bodily property of being well rounded