fluidity vs runniness

fluidity and runniness both are nouns.

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

As nouns, fluidity and runniness are synonyms defined as:

Other synonyms of fluidity include fluidness, liquidity, liquidness.

fluidity (noun)	runniness (noun)
the property of flowing easily	the property of flowing easily
a changeable quality