morganatic

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Of or being a legal marriage between a person of royal or noble birth and a partner of lower rank, in which it is agreed that no titles or estates of the royal or noble partner are to be shared by the partner of inferior rank nor by any of the offspring of the marriage.

from The Century Dictionary.

• An epithet noting a marriage of a man of high rank to a woman of lower station which is contracted with a stipulation that neither she nor the issue, if any, shall claim his rank or property in consequence; pertaining to a marriage of a woman of high rank to a man of lower station: hence applied also to a wife or a husband who has agreed to such a marriage contract.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Pertaining to, in the manner of, or designating, a kind of marriage, called also left-handed marriage, between a man of superior rank and a woman of inferior, in which it is stipulated that neither the latter nor her children shall enjoy the rank or inherit the possessions of her husband.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Designating a marriage (or the wife involved) between a man of higher rank and a woman of lower rank, often having various legal repercussions (typically that such a wife has no claim on the husband's possessions or title). It was not an aspect of English law, but was common in other royal houses, especially in Germany.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective (of marriages) of a marriage between one of royal or noble birth and one of lower rank; valid but with the understanding that the rank of the inferior remains unchanged and offspring do not succeed to titles or property of the superior