sadness vs poignancy

sadness and poignancy both are nouns.

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

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

Other hyponyms of sadness include bereavement, mourning, poignance.

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