crypto-Calvinist
/ˌkrɪptəʊˈkalvɪnɪst/Chiefly historical
noun
In 16th-cent. Germany: a Lutheran who secretly adheres to Calvinist principles; a Philippist, a Melanchthonian. Also more generally: any secret adherent of Calvinism.
Origin
Mid 18th century; earliest use found in Archibald Maclaine (1722–1804), Presbyterian minister and historian. From crypto- + Calvinist, partly after post-classical Latin crypto-Calvinista and German Kryptokalvinist, †Cryptokalvinist.