forehead: the brow above the eyes, the part of a person's face that cannot be hidden, and so the natural place for a mark, a wound, or a visible attitude
This is a small, concrete word: the brow, the stretch of the face above the eyes and below the hairline. It turns up only thirteen times in the Hebrew Bible, and every one of them means that same patch of skin. It is narrower than the whole face (פָּנִים), which covers everything a person turns toward you.
What gives the word its weight is that a brow is the part of a person nobody can cover. Whatever is put there, everyone sees:
- the gold plate reading "Holy to the LORD" that sat on the high priest's brow, so that Israel's offerings would be accepted
- the mark drawn on the foreheads of the few in Jerusalem who grieved over what their city had become
- the stone that sank into the giant's brow, and the skin disease that broke out on King Uzziah's while he stood at the incense altar
From there the language makes a short leap. If your brow is what you show the world, then a hard brow is a person who will not take anything in. Isaiah says Israel's forehead is bronze. Ezekiel calls his hearers hard of brow and pairs that with a stubborn heart. Jeremiah sharpens the picture into shamelessness: a brow like a prostitute's, a face that has forgotten how to blush. The closest neighbor of the image is the stiff neck (עֹרֶף), and Isaiah sets the two side by side in one breath.
The most striking use turns the insult into a gift. God tells Ezekiel that he has made the prophet's own brow hard, harder than the hardest stone, set against the hard brows of the people he is sent to. The very word that condemns his audience is what equips him to stand in front of them.