heftiness vs massiveness

heftiness and massiveness both are nouns.

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

As nouns, heftiness and massiveness are synonyms defined as:

Other synonyms of heftiness include heft, ponderosity, ponderousness.

heftiness (noun)	massiveness (noun)
possessing muscular strength	an unwieldy largeness
the property of being large in mass	the property of being large in mass