insufficiency vs inability

insufficiency and inability both are nouns.

Word	Noun	Adjective	Verb	Adverb
insufficiency	Yes	No	No	No
inability	Yes	No	No	No

As nouns, inability is a hypernym of insufficiency; that is, inability is a word with a broader meaning than insufficiency:

insufficiency: (pathology) inability of a bodily part or organ to function normally
inability: lacking the power to perform

Other hypernyms of insufficiency include unfitness.

insufficiency (noun)	inability (noun)
lack of an adequate quantity or number	lacking the power to perform
(pathology) inability of a bodily part or organ to function normally	lack of ability (especially mental ability) to do something
a lack of competence