The common misspelling of "Spider-Man".
Since this was mentioned in an episode of "Seinfeld" (where Jerry says "Spiderman" sounds like a Jewishname), it may have helped spread the misspelling.
NOTE: the hyphen "-" was put into the title/name to help distinguish "Spider-Man" from "Superman" on the comic book covers.
I was reading the a review of the latest Spider-Man comic and the idiot editor spelled it "Spiderman". Pfft.
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