thinness vs fluidity

thinness and fluidity both are nouns.

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

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

Other hyponyms of thinness include fluidness, liquidity, liquidness, runniness, wateriness.

thinness (noun)	fluidity (noun)
the property of having little body fat	the property of flowing easily
relatively small dimension through an object as opposed to its length or width	a changeable quality
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.