daylight: the light that beams out over a day, set directly against darkness
This word turns up once in the whole Bible, in Job's curse on the day he was born. Job asks that the day be handed over to darkness: that God overhead not go looking for it, and that no daylight ever break out over it again. The line puts this word squarely opposite darkness, so what it means is not really in doubt, even though we only ever get to see it used once.
Hebrew already had a plain, everyday word for light (אוֹר). Job's poem reaches instead for a rare form built on a root for shining that is far more at home in Aramaic, where the matching word (נְהִירוּ) is simply the ordinary term for light. That suits the book of Job, whose poetry is thick with unusual and foreign-sounding vocabulary. Scholars differ slightly over how narrow the word is: some read it as daylight in general, others as the first light of morning, close to the idea of daybreak (שַׁחַר).
Job 3 reads like creation running backwards. Where Genesis has God say "let there be light," Job says "let there be darkness," and this word names the daylight he wants cancelled. The verb beside it means to beam or shine out, so the picture is of morning light actively breaking over a day, which is exactly what the curse forbids.