Mess John is the old epithet in Scottish ballad poetry for a priest, derived from the celebration of the mass, so that "Mess John" signified in irreverent phrase, John who celebrated the mass. The English have a kindred phrase, "Jack Priest".
"The auld folk soon gied their consent, Wha ty'd them to their heart's content, And now she's Lady Gowrie" (The Lass o' Gowrie)References
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