| 1. | the time by which something must be finished or submitted; the latest time for finishing something: a five o'clock deadline. |
| 2. | a line or limit that must not be passed. |
| 3. | (formerly) a boundary around a military prison beyond which a prisoner could not venture without risk of being shot by the guards. |
"Seventeen feet from the inner stockade was the 'dead-line,' over which no man could pass and live." [Lossing, 1868]