sadness vs poignance

sadness and poignance both are nouns.

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

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

Other hyponyms of sadness include bereavement, mourning, poignancy.

sadness (noun)	poignance (noun)
the quality of excessive mournfulness and uncheerfulness	a state of deeply felt distress or sorrow
emotions experienced when not in a state of well-being
the state of being sad