aptitude vs ability

aptitude and ability both are nouns.

Word	Noun	Adjective	Verb	Adverb
aptitude	Yes	No	No	No
ability	Yes	No	No	No

As nouns, ability is a hypernym of aptitude; that is, ability is a word with a broader meaning than aptitude:

aptitude: inherent ability
ability: possession of the qualities (especially mental qualities) required to do something or get something done

Other hypernyms of aptitude include power.

aptitude (noun)	ability (noun)
inherent ability	the quality of being able to perform; a quality that permits or facilitates achievement or accomplishment
	possession of the qualities (especially mental qualities) required to do something or get something done