This compound adjective intensifies the sense of lethality, describing something that brings or carries death. More emphatic than simply 'deadly,' it suggests an active death-bearing quality. Classical usage applied it to fatal wounds, mortal diseases, poisonous plants, and capital trials. James uses it to describe the untamable tongue as 'a restless evil, full of deadly poison.' The term combines the noun for death with a root meaning 'to bear' or 'carry,' creating the image of something actively bringing death in its wake.