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2.
as in old news. when someone has just told you information that you already know.
Beni went all out telling me about the 13 year old father in the UK, but I knew about it already. This news is so yestersay!
by annie004 February 20, 2009
 
1.
A statement or piece of news that everyone knows, or is out-dated. To describe such a statement as "yestersay" is like discarding it as "so yesterday".
Lisa: "Hey, did you hear that Jane Doe is dropping out of the Republican race?"

John: "Dude, that's yestersay!"
by nurdsmith January 05, 2012
 
3.
Words spoken the day before, or prior.
"Just do it" is yestersay.
by PrairieDawg October 24, 2008