morganatic
: of, relating to, or being a marriage between a member of a royal or noble family and a person of inferior rank in which the rank of the inferior partner remains unchanged and the children of the marriage do not succeed to the titles, fiefs, or entailed property of the parent of higher rank
Can't say for sure. Yours doesn't seem to quite fit the bill but I can't find 'maritage' for a definition. I don't have Chambers, Bradford or the like though.
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