Douglas Harper's Etymology Dictionary
n. the doctrine that faith is the basis of all knowledge
Fideism is an epistemological theory which maintains that faith is independent of reason, or that reason and faith are hostile to each other and faith is superior at arriving at particular truths (see natural theology). The word fideism comes from fides, the Latin word for faith, and literally means "faith -ism."
Theologians and philosophers have responded in various ways to the place of faith and reason in determining the truth of metaphysical ideas, morality, and religious beliefs. A fideist is one who argues for fideism. Historically, fideism is most commonly ascribed to four philosophers: Pascal, Kierkegaard, William James, and Wittgenstein; with fideism being a label applied in a negative sense by their opponents, but which is not always supported by their own ideas and works or followers. There are a number of different forms of fideism.