big wheel vs knocker

big wheel and knocker both are nouns.

Word	Noun	Adjective	Verb	Adverb
big wheel	Yes	No	No	No
knocker	Yes	No	No	No

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

big wheel: an important influential person
knocker: (Yiddish) a big shot who knows it and acts that way; a boastful immoderate person

Other hyponyms of big wheel include supremo.

big wheel (noun)	knocker (noun)
an important influential person	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