thinness vs slightness

thinness and slightness both are nouns.

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

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

thinness (noun)	slightness (noun)
the property of having little body fat	slenderness
relatively small dimension through an object as opposed to its length or width	the property of an attractively thin person
a consistency of low viscosity	the quality of being unimportant and petty or frivolous
the property of being very narrow or thin
the property of being scanty or scattered; lacking denseness
The property of lacking substance or strength.