ponderousness vs ponderosity

ponderousness and ponderosity both are nouns.

Word	Noun	Adjective	Verb	Adverb
ponderousness	Yes	No	No	No
ponderosity	Yes	No	No	No

As nouns, ponderousness and ponderosity are synonyms defined as:

Other synonyms of ponderousness include heft, heftiness, massiveness.

ponderousness (noun)	ponderosity (noun)
the property of being large in mass	the property of being large in mass
an oppressive quality that is laborious and solemn and lacks grace or fluency