sweetness vs niceness

sweetness and niceness both are nouns.

Word	Noun	Adjective	Verb	Adverb
sweetness	Yes	No	No	No
niceness	Yes	No	No	No

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

Other hyponyms of sweetness include pleasingness, agreeableness, amenity, enjoyableness.

sweetness (noun)	niceness (noun)
the property of tasting as if it contains sugar	the quality of nice
a pleasingly sweet olfactory property	the quality of being difficult to detect or analyze
the quality of giving pleasure	a courteous manner that respects accepted social usage
the taste experience when sugar dissolves in the mouth