(theology, historical) A follower of Thomas Erastus (1524–1583), Swissphysician and theologian, or his doctrines, associated with the idea that the State should have supremacy in ecclesiastical matters.
1932, Duff Cooper, Talleyrand, Folio Society 2010, p. 96:Napoleon may not have believed in God, but he certainly believed in the desirability of religion, and, while his outlook was naturally Erastian, he was anxious from the first to restore normal relations with the Papacy.
