ponderousness vs heaviness

ponderousness and heaviness both are nouns.

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

As nouns, heaviness is a hypernym of ponderousness; that is, heaviness is a word with a broader meaning than ponderousness:

Other hypernyms of ponderousness include weightiness.

As nouns, ponderousness and heaviness are synonyms defined as:

ponderousness and heaviness: an oppressive quality that is laborious and solemn and lacks grace or fluency

ponderousness (noun)	heaviness (noun)
the property of being large in mass	the property of being comparatively great in weight
an oppressive quality that is laborious and solemn and lacks grace or fluency	used of a line or mark
	unwelcome burdensome difficulty
	an oppressive quality that is laborious and solemn and lacks grace or fluency
	persisting sadness