The word heaviness is a noun. It is an uncountable noun.
The part of speech for this particular word is a noun.
part of speech
The root word for heaviness is "heavy."
The abstract noun of "heavy" is "heaviness."
The part of speech for "answer" is a noun.
adverb
what part of speech is beneath
The heaviness of the truck tire was too much for me to pick up. The heaviness of the comment was too much to bear.
Height
Heaviness has three syllables. The syllables are heav-i-ness.
The object's heaviness was so much that I had to drop it before my arms fell off.
The part of speech for "unfamiliar" is an adjective.