heftiness vs ponderousness

heftiness and ponderousness both are nouns.

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

As nouns, heftiness and ponderousness are synonyms defined as:

Other synonyms of heftiness include heft, massiveness, ponderosity.

heftiness (noun)	ponderousness (noun)
possessing muscular strength	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