inflexibility vs inflexible

inflexibility is a noun but inflexible is not a noun.

Word	Noun	Adjective	Verb	Adverb
inflexibility	Yes	No	No	No
inflexible	No	Yes	No	No

inflexibility (noun)	inflexible (noun)
the quality of being rigid and rigorously severe
a lack of physical flexibility

inflexibility (adjective)	inflexible (adjective)
	resistant to being bent
	incapable of change
	not making concessions
	incapable of adapting or changing to meet circumstances