diagnosing vs diagnosis

diagnosing and diagnosis both are nouns.

Word	Noun	Adjective	Verb	Adverb
diagnosing	Yes	No	No	No
diagnosis	Yes	No	No	No

As nouns, diagnosing and diagnosis are synonyms defined as:

diagnosing and diagnosis: identifying the nature or cause of some phenomenon

diagnosing (noun)	diagnosis (noun)
identifying the nature or cause of some phenomenon	identifying the nature or cause of some phenomenon