ability vs attainment

ability and attainment both are nouns.

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

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

ability: possession of the qualities (especially mental qualities) required to do something or get something done
attainment: an ability that has been acquired by training

ability (noun)	attainment (noun)
the quality of being able to perform; a quality that permits or facilitates achievement or accomplishment	the act of achieving an aim
possession of the qualities (especially mental qualities) required to do something or get something done	arrival at a new stage
	an ability that has been acquired by training