went back to my 1983 Webster dictionary - 30 years ago. Won't do the whole thing - this is the full, 2,000+ page dictionary, unabridged, so it's a long definition. But some parts of it:
Marriage:
1. The state of being married; relation between husband and wife; married life; wedlock; matrimony
2. the act of marrying; wedding
3. the rite or form used in marrying
4. any close or intimate union.
Even back then, they don't specify opposite genders. "any close or intimate union".
Now of course you'll say they didn't think they had to back then... but yes, definitions change over time, and using the most recent one is most relevant to this discussion.
Just out of curiosity, I looked up "Troll" and there is NO reference to the internet; there are references to move in a circular direction; to sing rounds; to fish; and of course to supernatural beings. But nothing about internet behavior. AND in fact, there STILL is nothing about internet behaviour in the current definition -
Troll - Definition and More from the Free Merriam-Webster Dictionary
So we know internet trolls exist, even though the definition doesn't include them.
Marriage between same sex IS part of the definition; why does anyone deny it?