Morganatic Marriage, is a union permitted to German princes who, forbidden to marry except with one of equal rank, may ally themselves with a woman of inferior status, their children being legitimate but not eligible for the succession; the marriages of British princes contracted before the age of 25 without consent of the sovereign, or after that age without consent of Parliament, are of a morganatic nature.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Moreau, Jean Victor * Morgarten