Dictionary.com
definitions

establishmentarian

[ih-stab-lish-muh n-tair-ee-uh n]

adjective

of or relating to an established church, especially the Church of England, or the principle of state religion.
(often initial capital letter) of, relating to, or favoring a political or social establishment.

noun

a supporter or adherent of the principle of the establishment of a church by state law; an advocate of state religion.
(often initial capital letter) a person who belongs to or favors a political or social establishment.

Origin of establishmentarian

First recorded in 1840–50; establishment + -arian
Related formses·tab·lish·men·tar·i·an·ism, noun
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
British Dictionary definitions for establishmentarian

establishmentarian

adjective

denoting or relating to an Established Church, esp the Church of England
denoting or relating to the principle of a Church being officially recognized as a national institution

noun

an upholder of this principle, esp as applied to the Church of England
Derived Formsestablishmentarianism, noun
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Word Origin and History for establishmentarian
n.

"adherent of the principle of an established church," 1846, from establishment.

Online Etymology Dictionary, © 2010 Douglas Harper