WordNet
n. (New Testament) day of the Last Judgment when God will decree the fates of all men according to the good and evil of their earthly lives [syn: Judgment Day, Judgement Day, Day of Judgment, Day of Judgement, Doomsday, Last Judgment, Last Judgement, Last Day, day of reckoning, doomsday, end of the world]
Wikipedia
The Crack of Doom is an old term used for the Christian Day of Judgement, referring in particular to the blast of trumpets signalling the end of the world in Chapter 8 of the Book of Revelation. A "crack" had the sense of any loud noise, preserved in the phrase "crack of thunder", and Doom was a term for the Last Judgement, as Doomsday still is.
The phrase is famously used in the Day of Judgement sense by William Shakespeare in Macbeth, where on the heath the Three Witches show Macbeth the line of kings that will issue from Banquo:
'Why do you show me this? A fourth! Start, eyes! What, will the line stretch out to the crack of doom? Another yet! A seventh! I'll see no more:'(Act 4, scene 1, 112–117)- meaning that Banquo's line will endure until the Judgement Day, flattery for King James I, who claimed descent from Banquo.
Usage examples of "crack of doom".
The light sprang up again, and there on the brink of the chasm, at the very Crack of Doom, stood Frodo, black against the glare, tense, erect, but still as if he had been turned to stone.
But Gandalf tells him that it can only be destroyed in the volcano where it was made, in the Crack of Doom in Mordor.
I ~ould hear it pealing away through the empty bills like the crack of doom.
The tiny bit of encroaching blackness was perhaps the width of a fingernail, but to the staring watchers it magnified itself into the crack of doom.
But he'd gotten no further than ten yards away when a dazzling sizzle of lightning split the air like the crack of Doom.