rustiness vs rusty

rustiness is a noun but rusty is not a noun.

Word	Noun	Adjective	Verb	Adverb
rustiness	Yes	No	No	No
rusty	No	Yes	No	No

rustiness (noun)	rusty (noun)
ineptitude or awkwardness as a consequence of age or lack of practice
the condition of being coated or clogged with rust

rustiness (adjective)	rusty (adjective)
	of the brown color of rust
	ancient
	covered with or consisting of rust
	impaired in skill by neglect