unbendable vs stiff

unbendable is not a noun while stiff is a noun.

Word	Noun	Adjective	Verb	Adverb
unbendable	No	Yes	No	No
stiff	Yes	Yes	No	Yes

As adjectives, unbendable and stiff are synonyms defined as:

unbendable and stiff: marked by firm determination or resolution; not shakable

Other synonyms of unbendable include firm, steadfast, steady, unfaltering, unshakable, unwavering.

unbendable (noun)	stiff (noun)
	the dead body of a human being
	an ordinary man

unbendable (adjective)	stiff (adjective)
marked by firm determination or resolution; not shakable	having a strong physiological or chemical effect
	rigidly formal
	not moving or operating freely
	very drunk
	marked by firm determination or resolution; not shakable
	strong, vigorous
	incapable of or resistant to bending

unbendable (adverb)	stiff (adverb)
	in a stiff manner
	to a great degree