aptitude vs capability

aptitude and capability both are nouns.

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

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

Other hyponyms of aptitude include inherent aptitude, instinct, capableness, potentiality, natural ability.

aptitude (noun)	capability (noun)
inherent ability	the quality of being capable -- physically or intellectually or legally
	an aptitude that may be developed
	the susceptibility of something to a particular treatment