Deadline
wiktionary
According to the Oxford English Dictionary, early usage refers simply to lines that do not move, such as one used in angling. Slightly later American usage refers to a boundary in a prison which prisoners must not cross. There is only indirect evidence that the sense of "due date" may be connected with this use of the term in prison camps during the American Civil War, when it referred to a physical line or boundary beyond which prisoners were shot. [1] In fact, the term is no longer found in print by the end of the 19th century, but it soon resurfaces in writing in 1917 as a printing term for a guideline on the bed of a printing press beyond which text will not print. Three years later, the term is found in print in the sense of "time limit" in the closely connected publishing industry, indicating the time after which material would not make it into a newspaper or periodical. [2]
etymonline
deadline (n.)
"time limit," 1920, American English newspaper jargon, from dead (adj.) + line (n.). Perhaps influenced by earlier use (1864) to mean the "do-not-cross" line in Civil War prisons, which figured in the trial of Henry Wirz, commander of the notorious Confederate prison at Andersonville, Georgia.
And 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 the said "dead line" .... ["Trial of Henry Wirz," Report of the Secretary of War, Oct. 31, 1865]
