marriage... 4.any close or intimate union. —Webster’s New World Dictionary, 1957
I’d disagree in the modern sense, but it’s there.
While irreverent, that meaning was primarily used as slang or jargon or analogy, for example by Mergers and Acquisitions lawyers. Nobody who off-handedly used the term “marriage” to describe, for example, Abbott and Costello, deliberately intended to change the meaning of “marriage” in a legal or social sense.
The push for gay “marriage” is an ideological attempt to sacrilegiously change the original meaning of the word. Webster’s has signed up for that agenda, and is thus siding with our enemies. One wouldn’t imagine that, at the height of the Cold War, Webster’s would give a definition of “freedom” as “the state’s commitment to unite the proletariat”.