(A). A marriage in which the wife does not take the husband's rank, because legally, or according to court bye-laws, the marriage is not recognised. This sort of marriage is effected when a man of high rank marries a woman of inferior position. The children in this case do not inherit the title or entails of the father. The word is based on the Gothic morgjan, “to curtail” or “limit;” and the marriage settlement was called morgengabe or morgengnade, whence the Low Latin matrimonium ad legem morganaticam, in which the dowry is to be considered all the portion the wife will receive, as the estates cannot pass to her or to her children.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894