downheartedness vs sadness

downheartedness and sadness both are nouns.

Word	Noun	Adjective	Verb	Adverb
downheartedness	Yes	No	No	No
sadness	Yes	No	No	No

As nouns, sadness is a hypernym of downheartedness; that is, sadness is a word with a broader meaning than downheartedness:

Other hypernyms of downheartedness include unhappiness.

downheartedness (noun)	sadness (noun)
a feeling of low spirits	the quality of excessive mournfulness and uncheerfulness
	emotions experienced when not in a state of well-being
	the state of being sad