knocker vs sideboob

knocker and sideboob both are nouns.

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

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

knocker: either of two soft fleshy milk-secreting glandular organs on the chest of a woman
sideboob: A breast exposed from the side

knocker (noun)	sideboob (noun)
a device (usually metal and ornamental) attached by a hinge to a door	A breast exposed from the side
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