thinness vs skinniness

thinness and skinniness both are nouns.

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

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

thinness (noun)	skinniness (noun)
the property of having little body fat	the bodily property of lacking flesh
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.