Legend has it the name means "spite the devil." from the Dutch, who of course originally settled New Amsterdam, specifically lower Manhattan, later renamed New York. Here is the northern tip of Manhattan, the bridge connecting us with the lower portion of Riverdale, in the Bronx. Another legend that I've never verified, is that this waterway (the portion that connects the "East River" with the Hudson River) was moved from a point further north. That is, the lower section of Riverdale was once part of Manhattan, and even retains its 212 area code for this reason. This was told to me by a geology professor at City College some years ago, as I remember it.
So I guess I should do a little research before posting these things!
This is actually the Henry Hudson Bridge, which I've traveled scores of times just in the last couple of years, and I never bothered to notice its real name, because somewhere long ago I heard it referred to by someone as the Spuyten Duyvil Bridge, and the name just stuck. There must be signs as you approach the bridge alerting you to its true name, but it just never registered in my brain. Funny how that works.
The Spuyten Duyvil Bridge is a small Amtrak railroad bridge just to the west of the Henry Hudson Bridge.
Then there is a small section of Riverdale (which is, remember, a small section of the Bronx) called "Marble Hill," and which was in fact once physically connected to Manhattan and separated by hook in the Harlem River from the Bronx. That hook proved to be a difficult shipping passage and thus the river was re-routed through Marble Hill, separating it from Manhattan. Eventually the original path of the river was filled in and built on. Administratively, Marble Hill is still part of Manhattan and New York County (not Bronx County)
Hope I got all that right this time. Take a look at the maps linked to above, it all makes sense.