cynic vs knocker

cynic and knocker both are nouns.

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

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

Other hyponyms of cynic include depreciator, detractor, disparager.

cynic (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