thinness vs slenderness

thinness and slenderness both are nouns.

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

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

As nouns, thinness and slenderness are synonyms defined as:

thinness and slenderness: relatively small dimension through an object as opposed to its length or width

Other synonyms of thinness include tenuity.

thinness (noun)	slenderness (noun)
the property of having little body fat	the quality of being slight or inadequate
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	relatively small dimension through an object as opposed to its length or width
the property of being very narrow or thin
the property of being scanty or scattered; lacking denseness
The property of lacking substance or strength.