One theory says that it was based on the French word or, meaning gold, because the original package was gold in color. Then, since the original cookie was mound-shaped, another theory points to the Greek word for mountain, oros. It appears in English as the root oro-, but that would be like calling a pimple Mount Everest.
Another theory says that the O represented the shape of the cookie, so it shows up twice in the word, with -re- stuffed between as a shortened form of cream. But that's unrecognizable; surely, they would have retained -cre-.
I have two bogus contributions to add to folk etymology. First, the word re in Latin means again or repeatedly, so Oreo could be translated as O-repeat-O. Second, yet another Greek form that has worked its way into English has the form oro-. It means mouth; what could be more appropriate?
If anyone has a documented origin, fire away.
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