A noun meaning priest — one who serves as a mediator between the human community and the divine, offering sacrifices, maintaining holy space, and performing sacred rites. In the New Testament it refers to Jewish priests, Gentile priests, and supremely to Jesus as the ultimate high priest in Hebrews.
Hiereus is the Greek word at the center of the entire sacrificial system. The priest's role was mediatorial: standing between holy God and sinful humanity, offering blood that covered transgression. Hebrews develops the priesthood of Jesus with extraordinary depth — he is a priest after the order of Melchizedek, superior to the Levitical priests, who offered himself as the ultimate sacrifice once for all. His priesthood is permanent — he ever lives to intercede. The priest who needed daily to atone for his own sins has been replaced by the sinless priest whose sacrifice never needs repeating.