detractor vs knocker

detractor and knocker both are nouns.

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

As nouns, detractor and knocker are synonyms defined as:

detractor and knocker: one who disparages or belittles the worth of something

Other synonyms of detractor include depreciator, disparager.

detractor (noun)	knocker (noun)
one who disparages or belittles the worth of something	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