faultfinder vs knocker

faultfinder and knocker both are nouns.

Word	Noun	Adjective	Verb	Adverb
faultfinder	Yes	No	No	No
knocker	Yes	No	No	No

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

Other hyponyms of faultfinder include depreciator, detractor, disparager.

faultfinder (noun)	knocker (noun)
someone who is critical of the motives of others	a device (usually metal and ornamental) attached by a hinge to a door
	either of two soft fleshy milk-secreting glandular organs on the chest of a woman
	one who disparages or belittles the worth of something
	a person who knocks (as seeking to gain admittance)
	(Yiddish) a big shot who knows it and acts that way; a boastful immoderate person