heaviness vs weightiness

heaviness and weightiness both are nouns.

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

As nouns, heaviness and weightiness are synonyms defined as:

heaviness and weightiness: the property of being comparatively great in weight

heaviness (noun)	weightiness (noun)
the property of being comparatively great in weight	the property of being comparatively great in weight
used of a line or mark	the relative importance granted to something
unwelcome burdensome difficulty
an oppressive quality that is laborious and solemn and lacks grace or fluency
persisting sadness