'establishmentarian' originates from Modern English, formed from 'establishment' + the suffix '-arian' (from Latin '-arius' meaning 'pertaining to'), indicating a person who supports the establishment.

'establishment' developed from Old French 'establissement' and Latin roots related to 'stabilis'/'stabilire' ('to make firm, establish'), and the agent-forming suffix '-arian' came via Latin '-arius' and later English usage; the compound 'establishmentarian' arose in English usage in the 19th century.

Initially it denoted someone who supported established institutions (especially the established church); over time it has retained that basic sense and is used broadly for supporters of the status quo.