clumsiness vs rustiness

clumsiness and rustiness both are nouns.

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

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

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

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

clumsiness (noun)	rustiness (noun)
the carriage of someone whose movements and posture are ungainly or inelegant	ineptitude or awkwardness as a consequence of age or lack of practice
the inelegance of someone stiff and unrelaxed (as by embarrassment)	the condition of being coated or clogged with rust
unskillfulness resulting from a lack of training