slightness vs spareness

slightness and spareness both are nouns.

Word	Noun	Adjective	Verb	Adverb
slightness	Yes	No	No	No
spareness	Yes	No	No	No

As nouns, spareness is a hypernym of slightness; that is, spareness is a word with a broader meaning than slightness:

Other hypernyms of slightness include leanness, thinness.

slightness (noun)	spareness (noun)
slenderness	the property of being scanty or scattered; lacking denseness
the property of an attractively thin person	the property of having little body fat
the quality of being unimportant and petty or frivolous