massiveness vs heaviness

massiveness and heaviness both are nouns.

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

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

Other hypernyms of massiveness include weightiness.

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