big wheel vs big fish

big wheel and big fish both are nouns.

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

As nouns, big wheel and big fish are synonyms defined as:

Other synonyms of big wheel include big cheese, big deal, big enchilada, big gun, big shot, head honcho.

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