trite from having long been used or known.
Origin of old hat
First recorded in 1745–55
Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
British Dictionary definitions for old hat
(postpositive) old-fashioned or trite
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
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Word Origin and History for old hat
"out of date," first recorded 1911. As a noun phrase, however, it had different sense previously. The "Classical Dictionary of the Vulgar Tongue" (1796) defines it as, "a woman's privities, because frequently felt."
Online Etymology Dictionary, © 2010 Douglas Harper
Obsolete, old-fashioned: “Get with it, Murray; your methods are strictly old hat.”
The New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.