Job 3:5 - Matthew Poole's English Annotations on the Holy Bible

Darkness and the shadow of death, i.e. a black and dark shadow, like that of the place of the dead, which is a land of darkness, and where the light is darkness, as Job explains this very phrase, Job 10:21,22; or so gross and palpable darkness, that by its horrors and damps may take away men's spirits and lives. Stain it, i.e. take away its beauty and glory, and make it abominable, as a filthy thing. Or, challenge it, i.e. take and keep the entire possession of it, so as the light may not have the least share in it. Terrify it, to wit, the day, i.e. men in it. Let it be always observed as a frightful and dismal day.