weakness vs inadequacy

weakness and inadequacy both are nouns.

Word	Noun	Adjective	Verb	Adverb
weakness	Yes	No	No	No
inadequacy	Yes	No	No	No

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

Other hyponyms of weakness include insufficiency, fatigue, flaw.

weakness (noun)	inadequacy (noun)
the property of lacking physical or mental strength; liability to failure under pressure or stress or strain	unsatisfactoriness by virtue of being inadequate
powerlessness revealed by an inability to act	lack of an adequate quantity or number
a penchant for something even though it might not be good for you	a lack of competence
a flaw or weak point
the condition of being financially weak