knocker vs backbiter

knocker and backbiter both are nouns.

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

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

Other hyponyms of knocker include defamer, libeler, maligner, slanderer, traducer, vilifier, hatemonger, muckraker, mudslinger.

knocker (noun)	backbiter (noun)
a device (usually metal and ornamental) attached by a hinge to a door	one who attacks the reputation of another by slander or libel
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