aptness vs disposition

aptness and disposition both are nouns.

Word	Noun	Adjective	Verb	Adverb
aptness	Yes	No	No	No
disposition	Yes	No	No	No

As nouns, disposition is a hypernym of aptness; that is, disposition is a word with a broader meaning than aptness:

aptness: a disposition to behave in a certain way
disposition: a natural or acquired habit or characteristic tendency in a person or thing

aptness (noun)	disposition (noun)
appropriateness for the occasion	the act or means of getting rid of something
a disposition to behave in a certain way	your usual mood
	a natural or acquired habit or characteristic tendency in a person or thing
	an attitude of mind especially one that favors one alternative over others