business vs business sector

business and business sector both are nouns.

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

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

business (noun)	business sector (noun)
the principal activity in your life that you do to earn money	business concerns collectively
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