What does "commonly-held" mean here?
The phrase "commonly-held" means to be believed by a lot of people. So here, "commonly-held" indicates that the myths are believed and thought to be true by many people. Here's a few examples of some more uses of "commonly-held": Ex: The most commonly-held opinion among my family is that education is important. Ex: A hundred years ago, it was commonly-held that women should not have voting rights.