business line vs line of business

business line and line of business both are nouns.

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

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

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

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

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