smallness vs slightness

smallness and slightness both are nouns.

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

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

smallness (noun)	slightness (noun)
the property of having a relatively small size	slenderness
lack of generosity in trifling matters	the property of an attractively thin person
the property of being a relatively small amount	the quality of being unimportant and petty or frivolous
the property of having relatively little strength or vigor
The quality of being minor in influence, power, or rank.