rigid vs rigidity

rigid is not a noun while rigidity is a noun.

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

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

rigid (adjective)	rigidity (adjective)
designating an airship or dirigible having a form maintained by a stiff unyielding frame or structure
incapable of or resistant to bending
incapable of compromise or flexibility
fixed and unmoving
incapable of adapting or changing to meet circumstances