line of business vs business line

line of business and business line both are nouns.

Word	Noun	Adjective	Verb	Adverb
line of business	Yes	No	No	No
business line	Yes	No	No	No

As nouns, line of business and business line are synonyms defined as:

line of business and business line: a particular kind of product or merchandise

Other synonyms of line of business include line, line of merchandise, line of products, product line.

line of business (noun)	business line (noun)
a particular kind of commercial enterprise	a particular kind of product or merchandise
a particular kind of product or merchandise