An Etymological Dictionary of Astronomy and Astrophysics

The time by which something must be finished or submitted; the latest time for finishing something (Dictionary.com).

Etymology (EN): Historically, during the American Civil War, the term referred to a physical line or boundary beyond which prisoners were shot; → dead; → line.

Etymology (PE): Ruzband, literally “day lock, that which blocks date,” from ruz, → day, + band, → bond; cf. Ger. Stichtag, Anmeldeschluss, Einsendeschluss and Fr. date de clôture.