business sector vs business

business sector and business both are nouns.

Word	Noun	Adjective	Verb	Adverb
business sector	Yes	No	No	No
business	Yes	No	No	No

As nouns, business sector and business are synonyms defined as:

business sector (noun)	business (noun)
business concerns collectively	the principal activity in your life that you do to earn money
	the activity of providing goods and services involving financial and commercial and industrial aspects
	the volume of commercial activity
	incidental activity performed by an actor for dramatic effect
	an immediate objective
	a rightful concern or responsibility
	a commercial or industrial enterprise and the people who constitute it
	customers collectively
	business concerns collectively