thickness vs heaviness

thickness and heaviness both are nouns.

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

As nouns, thickness and heaviness are synonyms defined as:

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