the study or a course of study of history before the end of the Western Roman Empire a.d. 476.
information or an event of the recent past that is common knowledge or is no longer pertinent: Last week's news is ancient history.
an event, as in a person's life, that occurred in the remote past and has no practical relationship with the present: She was my best friend in high school, but that's ancient history now.
Origin of ancient history
First recorded in 1585–95
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
the history of the ancient world from the earliest known civilizations to the collapse of the Western Roman Empire in 476 a.d
informal a recent event or fact sufficiently familiar to have lost its pertinence
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
A past event, as in She's talking about her sea voyage, but that's ancient history, or And then there was his divorce, but you don't want to hear ancient history. This hyperbolic idiom transfers the field of ancient history to a much-repeated tale.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.