Deadline

I don’t think there’s a consensus about its origin, but one theory dates it back to a prisoner-of-war camp run during America’s Civil War in Defense of Slavery. In the trial of its commander, the Confederate Henry Wirz, the accusation was:

> [He], the said Wirz, still wickedly pursuing his evil purpose, did establish and cause to be designated within the prison enclosure containing said prisoners a "dead line," being a line around the inner face of the stockade or wall enclosing said prison and about twenty feet distant from and within said stockade; and so established said dead line, which was in many places an imaginary line, in many other places marked by insecure and shifting strips of [boards nailed] upon the tops of small and insecure stakes or posts, he, the said Wirz, instructed the prison guard stationed around the top of said stockade to fire upon and kill any of the prisoners aforesaid who might touch, fall upon, pass over or under [or] across said "dead line”.

One can imagine Wirz, talking to the person responsible for building a new stockade, saying, “It must be done by next Tuesday. Consider that date your dead line.” That would have been a metaphorical way of saying “Finishing by Tuesday is really, really important.” Suppose the term caught on at the camp. Then, when the pro-slavery side lost the war, and the jailers went home, they might have kept using it. At first, people would reply “huh?” to the phrase “dead line,” and the speaker would tell the story. At least at first. But how many times do you want to do that? It’s easier just to say “it’s a word that means when something has to be done - its due date.” And thus the metaphor makes the transition into just another vocabulary word.