Also, if you know anything about dictionaries and how to read them, a word when used, only has to meet one of the criteria to be acceptable.
Also, marriage means several different things. They don't have to CHANGE the definition, they can simply add a number.
marriage
-noun
1. the social institution under which a man and woman establish their decision to live as husband and wife by legal commitments, religious ceremonies, etc.
2. the state, condition, or relationship of being married; wedlock: a happy marriage.
3. the legal or religious ceremony that formalizes the decision of a man and woman to live as husband and wife, including the accompanying social festivities: to officiate at a marriage.
4. a relationship in which two people have pledged themselves to each other in the manner of a husband and wife, without legal sanction: trial marriage; homosexual marriage.
5. any close or intimate association or union: the marriage of words and music in a hit song.
6. a formal agreement between two companies or enterprises to combine operations, resources, etc., for mutual benefit; merger.
7. a blending or matching of different elements or components: The new lipstick is a beautiful marriage of fragrance and texture.
8. Cards. a meld of the king and queen of a suit, as in pinochle. Compare royal marriage.
9. a piece of antique furniture assembled from components of two or more authentic pieces.
One of them already can be interperated as such. It's considered a marriage. Notice how as our language evolved, more numbers get put on the list.