sincerity vs heartiness

sincerity and heartiness both are nouns.

Word	Noun	Adjective	Verb	Adverb
sincerity	Yes	No	No	No
heartiness	Yes	No	No	No

As nouns, heartiness is a hyponym of sincerity; that is, heartiness is a word with a more specific, narrower meaning than sincerity:

sincerity: the quality of being open and truthful; not deceitful or hypocritical
heartiness: the quality of hearty sincerity

Other hyponyms of sincerity include wholeheartedness, singleness, straightforwardness.

sincerity (noun)	heartiness (noun)
the quality of being open and truthful; not deceitful or hypocritical	the quality of hearty sincerity
the trait of being serious	active strength of body or mind
a quality of naturalness and simplicity
an earnest and sincere feeling