The antonym for postdating is "antedating," which means to assign an earlier date to something than the actual date. Antedating is often used in historical research to correct misplaced events, but it can also be used to deceive or manipulate. Another antonym for postdating is "dating," which simply refers to assigning a date to something without any particular temporal relation. Dating can be used in a variety of contexts, from personal relationships to official documentation. Finally, a more general antonym for postdating is "pre-dating," which refers to anything that occurs before a particular date or event. Pre-dating can be used in the context of history, relationships, or any situation where a chronological order is important.