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dumb (something) down
To make something less complicated to accommodate a less intelligent, educated, or sophisticated audience. The professor decided to dumb down the course material a bit after most of his class failed the first exam. I think we ought to dumb the play down a bit; after all, most of the people coming to see it won't have a PhD in drama.
To simplify something excessively in order to make it suitable for a less educated or less sophisticated audience: The researchers dumbed down the report before releasing it to the public.