According to my definition, a fundamentalist is someone who prefers to take knowledge from authority rather than from experience.
Creationists are the textbook case of fundamentalism. They'll spare no effort to discredit the science that falsifies literal biblical claims, but spend no effort justifying their belief in the authority of the Bible. If they were as skeptical of the Bible as they were of radiological dating, they would quickly denounce the Bible as a work of fiction.
Fundamentalism is not just another form of irrationality. It's irrationality with conviction. Fundamentalism has no corrective mechanism. How does the fundamentalist know that his authority is, well, authoritative? Apparently, not by experience. Without correction, we cannot claim commitment to the truth because we reject a priori any possibility that we could be wrong.
The Christian fundamentalist cannot complain that Osama bin Laden is using the wrong epistemology. bin Laden is using the very same epistemology as Jerry Falwell and Pat Robertson. Reason and experience are equally unimportant to all three of these clowns because each will carefully fold his experience to fit into his holy box.
The problem with every fundamentalism is that it results in unnecessary conflict. Instead of reaching consensus based on shared experience, the fundamentalist regards shared experience as either threatening or subservient to his unchangeable prior beliefs.