Arafel: A Hebrew word (ערפל), meaning 'fog'; generally used in reference to the Apocalypse. Possibly derived from Exodus 13:21 *The Lord preceded them... by means of a column of cloud to show them the way, and at night by means of a column of fire to give them light. or Job 22:13 *And thou sayest: 'What doth God know? Can He judge through the dark cloud?
Now the second quote about judgement from the Book of Job is obviously referenced in the definition of arafel as the "could-darkness of holy judgement" (GEoD). What really surprised me is that Exodus is almost literally quoted in Dune:
Leto stood in the foyer of his house, studying a note by the light of a single suspensor lamp. Dawn was yet a few hours away, and he felt his tiredness. A Fremen messenger had brought the note to the outer guard just now as the Duke arrived from his command post.
The note read: "A column of smoke by day, a pillar of fire by night."
I don't know if this was brought up before (in which case it completely escaped my attention), but this means that FH referenced arafel or at least had this concept on his mind long before writing GEoD.