Mid 15th century, from earlier parishen (c. 1200), from Old French paroissien, parochien, from paroisse (English parish). Equivalent to parish + -ian + -er.
parishioner (plural parishioners)
One of three common words containing shion, which are cushion, fashion, and parishioner. A variant spelling of the obsolete earlier form was parishion, which gives a third historical English word ending in -shion, not simply containing it.