expertise vs expertness

expertise and expertness both are nouns.

Word	Noun	Adjective	Verb	Adverb
expertise	Yes	No	No	No
expertness	Yes	No	No	No

As nouns, expertise and expertness are synonyms defined as:

expertise and expertness: skillfulness by virtue of possessing special knowledge

expertise (noun)	expertness (noun)
skillfulness by virtue of possessing special knowledge	skillfulness by virtue of possessing special knowledge