An exerpt from Cracked.com:
Fundamental refers to the Latin, "Fundamentum," which meant ass, which is the body's foundation, since both the basement and the ass is where many people store their unwanted possessions (i.e. "Junk in the trunk"). Or something like that.
Fortunately, this is not well known, as the "Reading is Fundamental" organization would have to explain to children that their slogan does not mean that reading is for assholes.
This nicely explains the meaning of "Fundamentalist," don't you think?