rustiness vs ineptness

rustiness and ineptness both are nouns.

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

As nouns, ineptness is a hypernym of rustiness; that is, ineptness is a word with a broader meaning than rustiness:

rustiness: ineptitude or awkwardness as a consequence of age or lack of practice
ineptness: unskillfulness resulting from a lack of training

Other hypernyms of rustiness include awkwardness, clumsiness, ineptitude, maladroitness, slowness.

rustiness (noun)	ineptness (noun)
ineptitude or awkwardness as a consequence of age or lack of practice	the quality of having the wrong properties for a specific purpose
the condition of being coated or clogged with rust	unskillfulness resulting from a lack of training