Boyd’s Bible Dictionary:

Unveiled women “hard of forehead

Concise Bible Dictionary:

2. metsach, μἐτωπον, used as a symbol of manifest character. Israel in apostasy is described as having a harlot's forehead, and refusing to be ashamed (Jer. 3:33Therefore the showers have been withholden, and there hath been no latter rain; and thou hadst a whore's forehead, thou refusedst to be ashamed. (Jeremiah 3:3)). Ezekiel's forehead was made as hard as adamant, because of the hardness of Israel's forehead, with whom he had to contend (Ezek. 3:8-98Behold, I have made thy face strong against their faces, and thy forehead strong against their foreheads. 9As an adamant harder than flint have I made thy forehead: fear them not, neither be dismayed at their looks, though they be a rebellious house. (Ezekiel 3:8‑9)). Aaron wore a plate of gold on his forehead, with “Holiness to the Lord” engraved thereon, that he might bear the iniquity of the holy things which the children of Israel should offer (Ex. 28:36-3836And thou shalt make a plate of pure gold, and grave upon it, like the engravings of a signet, HOLINESS TO THE LORD. 37And thou shalt put it on a blue lace, that it may be upon the mitre; upon the forefront of the mitre it shall be. 38And it shall be upon Aaron's forehead, that Aaron may bear the iniquity of the holy things, which the children of Israel shall hallow in all their holy gifts; and it shall be always upon his forehead, that they may be accepted before the Lord. (Exodus 28:36‑38)). God set a mark upon the foreheads of those that sighed and cried for the abominations that were done in Jerusalem, and the rest of the inhabitants were to be slain (Ezek. 9:4, 64And the Lord said unto him, Go through the midst of the city, through the midst of Jerusalem, and set a mark upon the foreheads of the men that sigh and that cry for all the abominations that be done in the midst thereof. (Ezekiel 9:4)
6Slay utterly old and young, both maids, and little children, and women: but come not near any man upon whom is the mark; and begin at my sanctuary. Then they began at the ancient men which were before the house. (Ezekiel 9:6)
). So, in a future day the servants of God will have His mark in their foreheads; Satan will also cause his followers to have a mark on their right hands or on their foreheads. All will then have to be manifest as to whom they belong (Rev. 7:33Saying, Hurt not the earth, neither the sea, nor the trees, till we have sealed the servants of our God in their foreheads. (Revelation 7:3); Rev. 9:44And it was commanded them that they should not hurt the grass of the earth, neither any green thing, neither any tree; but only those men which have not the seal of God in their foreheads. (Revelation 9:4); Rev. 13:1616And he causeth all, both small and great, rich and poor, free and bond, to receive a mark in their right hand, or in their foreheads: (Revelation 13:16); Rev. 14:1, 91And I looked, and, lo, a Lamb stood on the mount Sion, and with him an hundred forty and four thousand, having his Father's name written in their foreheads. (Revelation 14:1)
9And the third angel followed them, saying with a loud voice, If any man worship the beast and his image, and receive his mark in his forehead, or in his hand, (Revelation 14:9)
; Rev. 17:55And upon her forehead was a name written, MYSTERY, BABYLON THE GREAT, THE MOTHER OF HARLOTS AND ABOMINATIONS OF THE EARTH. (Revelation 17:5); Rev. 20:44And I saw thrones, and they sat upon them, and judgment was given unto them: and I saw the souls of them that were beheaded for the witness of Jesus, and for the word of God, and which had not worshipped the beast, neither his image, neither had received his mark upon their foreheads, or in their hands; and they lived and reigned with Christ a thousand years. (Revelation 20:4)).