massiveness vs heftiness

massiveness and heftiness both are nouns.

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

As nouns, massiveness and heftiness are synonyms defined as:

Other synonyms of massiveness include heft, ponderosity, ponderousness.

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