sept vs family line

sept and family line both are nouns.

Word	Noun	Adjective	Verb	Adverb
sept	Yes	No	No	No
family line	Yes	No	No	No

As nouns, sept and family line are synonyms defined as:

Other synonyms of sept include family, folk, kinfolk, kinsfolk, phratry.

sept (noun)	family line (noun)
people descended from a common ancestor	people descended from a common ancestor