plumpness vs buxomness

plumpness and buxomness both are nouns.

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

As nouns, buxomness is a hyponym of plumpness; that is, buxomness is a word with a more specific, narrower meaning than plumpness:

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

Other hyponyms of plumpness include chubbiness, pudginess, rolypoliness, tubbiness.

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