ineptitude vs rustiness

ineptitude and rustiness both are nouns.

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

As nouns, rustiness is a hyponym of ineptitude; that is, rustiness is a word with a more specific, narrower meaning than ineptitude:

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

Other hyponyms of ineptitude include ham-fistedness, ham-handedness, heavy-handedness.

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