adj. When one surrounds him/herself exclusively with those of similar religious beliefs to the extent that he/she begins to confuse baseless faith with proven knowledge.
The pastor leads such a hermetitheistic life that it's almost impossible for his new neighbor to to make smalltalk with him.
n 1: a person who holds religious beliefs in conflict with the dogma of the Roman Catholic Church syn: misbeliever, religious outcast
2: a person who holds unorthodox opinions in any field (not merely religion)