I'm searching for a certain single, rare, literary word meaning "something taken as truth due to having been repeated so much". This "something" could be either true or false. It is not necessarily pernicious or benign.
An example of such a "something" (at the risk of getting political) is that Osama Bin Laden was killed in May 2011.
Does anyone know the word I'm searching for?
P.S.: "Factoid" is ticked — however, there may exist an even better fit.