heaviness vs thickness

heaviness and thickness both are nouns.

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

As nouns, heaviness and thickness are synonyms defined as:

heaviness (noun)	thickness (noun)
the property of being comparatively great in weight	the dimension through an object as opposed to its length or width
used of a line or mark	resistance to flow
unwelcome burdensome difficulty	used of a line or mark
an oppressive quality that is laborious and solemn and lacks grace or fluency	indistinct articulation
persisting sadness