rigidity vs rigidness

rigidity and rigidness both are nouns.

Word	Noun	Adjective	Verb	Adverb
rigidity	Yes	No	No	No
rigidness	Yes	No	No	No

As nouns, rigidity and rigidness are synonyms defined as:

rigidity and rigidness: the physical property of being stiff and resisting bending

As nouns, rigidity and rigidness are synonyms defined as:

rigidity and rigidness: the quality of being rigid and rigorously severe

Other synonyms of rigidity include inflexibility.

rigidity (noun)	rigidness (noun)
the physical property of being stiff and resisting bending	the physical property of being stiff and resisting bending
the quality of being rigid and rigorously severe	the quality of being rigid and rigorously severe