competency vs fitness

competency and fitness both are nouns.

Word	Noun	Adjective	Verb	Adverb
competency	Yes	No	No	No
fitness	Yes	No	No	No

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

competency: the quality of being adequately or well qualified physically and intellectually
fitness: the quality of being qualified

Other hyponyms of competency include linguistic competence, proficiency.

competency (noun)	fitness (noun)
the quality of being adequately or well qualified physically and intellectually	the quality of being suitable
	the quality of being qualified
	good physical condition; being in shape or in condition