big businessman vs business leader

big businessman and business leader both are nouns.

Word	Noun	Adjective	Verb	Adverb
big businessman	Yes	No	No	No
business leader	Yes	No	No	No

As nouns, big businessman and business leader are synonyms defined as:

big businessman and business leader: a very wealthy or powerful businessman

Other synonyms of big businessman include baron, king, magnate, mogul, power, top executive, tycoon.

big businessman (noun)	business leader (noun)
a very wealthy or powerful businessman	a very wealthy or powerful businessman