skinniness vs thinness

skinniness and thinness both are nouns.

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

As nouns, thinness is a hypernym of skinniness; that is, thinness is a word with a broader meaning than skinniness:

Other hypernyms of skinniness include leanness, spareness.

skinniness (noun)	thinness (noun)
the bodily property of lacking flesh	the property of having little body fat
	relatively small dimension through an object as opposed to its length or width
	a consistency of low viscosity
	the property of being very narrow or thin
	the property of being scanty or scattered; lacking denseness
	The property of lacking substance or strength.