Mark 9:43

Into hell, into the unquenchable fire

(εις την γεενναν, εις το πυρ το ασβεστον). Not Hades, but Gehenna. Ασβεστον is alpha privative and σβεστος from σβεννυμ to quench. It occurs often in Homer. Our word asbestos is this very word. Matthew 18:8 has "into the eternal fire." The Valley of Hinnom had been desecrated by the sacrifice of children to Moloch so that as an accursed place it was used for the city garbage where worms gnawed and fires burned. It is thus a vivid picture of eternal punishment.