of noble birth; of rank
Literary expression meaning someone is of high social standing or distinguished lineage. Often used in classical or formal contexts.
彼は由有る家柄の出だ。
He comes from a family of noble birth.
The expression 由有る (よしある) combines 由 (reason, origin) and 有る (to exist), literally meaning 'having a (distinguished) origin'. The exact historical derivation is uncertain, but it is conventionally associated with noble lineage.