stiff vs unbendable

stiff is a noun but unbendable is not a noun.

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

As adjectives, stiff and unbendable are synonyms defined as:

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

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

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

stiff (adjective)	unbendable (adjective)
having a strong physiological or chemical effect	marked by firm determination or resolution; not shakable
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

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