rustiness vs ineptitude

rustiness and ineptitude both are nouns.

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

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

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

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

rustiness (noun)	ineptitude (noun)
ineptitude or awkwardness as a consequence of age or lack of practice	having no qualities that would render it valuable or useful
the condition of being coated or clogged with rust	unskillfulness resulting from a lack of training