inadequacy vs inadequateness

inadequacy and inadequateness both are nouns.

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

As nouns, inadequacy and inadequateness are synonyms defined as:

inadequacy and inadequateness: unsatisfactoriness by virtue of being inadequate

inadequacy (noun)	inadequateness (noun)
unsatisfactoriness by virtue of being inadequate	unsatisfactoriness by virtue of being inadequate
lack of an adequate quantity or number
a lack of competence