backdate

[ bak-deyt ]
/ ˈbækˌdeɪt /

verb (used with object), back·dat·ed, back·dat·ing.

to date earlier than the actual date; predate; antedate: Backdate the letter so he'll think I wrote it last week.

Origin of backdate

An Americanism dating back to 1945–50; back2 + date1
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for back-dated

backdate

/ (ˌbækˈdeɪt) /

verb

(tr) to make effective from an earlier datethe pay rise was backdated to August
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012