godan verb (-su)
say repeatedly; say proverbially
Used when a phrase or saying has been repeated so often that it has become a cliché or a well-known proverb. Often implies the expression is now trite or hackneyed.
「時は金なり」は言い古された言葉だ。
"Time is money" is a hackneyed phrase.
そんな言い古された理屈では
Nobody will be convinced by such a worn-out argument.