彼の家は名門の庶流にあたる。
His family is a cadet branch of a distinguished house.
嫡流が絶えたため、庶流から跡継ぎが迎えられた。
Because the main line died out, an heir was brought in from a branch family.
その武将は源氏の庶流の出と伝えられている。
That warlord is said to have come from a collateral line of the Minamoto clan.