Write "January 15" on a check you hand to someone on January 3, for example

• Assign to a later time
• Possibly mark payment for next month in office appointment
• Occur later than
• Put 12/31/2020 on checks, say
• Follow in time
• Write a check for later

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Postdate \Post"date`\, n. A date put to a bill of exchange or other paper, later than that when it was actually made.

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
also post-date , 1620s, from post- + date (v.1) "to assign a date to, to mark a date on." Related: Postdated ; postdating . Intransitive meaning "be of an earlier date" is from 1909.

Wiktionary Word definitions in Wiktionary
(context obsolete English) postdated; made or done after the date assigned. v 1 (context transitive English) To occur after an event or time; to exist later on in time 2 (context transitive English) To assign an effective date to a document or action later ...