fitness vs fettle

fitness and fettle both are nouns.

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

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

fitness (noun)	fettle (noun)
the quality of being suitable	a state of fitness and good health
the quality of being qualified
good physical condition; being in shape or in condition

fitness (verb)	fettle (verb)
	remove mold marks or sand from (a casting)