One often hears the argument made by opponents to same-sex marriage that the word “marriage” has a specific meaning, and that meaning does not encompass same-sex unions, and that therefore, same-sex unions, if they’re allowed at all, ought to be called by a different name.
Now, it’s true, of course, that the word “marriage” has a meaning, but a simple test will demonstrate that that meaning does, in fact, apply to same-sex couples. Namely, if I refer to a same-sex marriage, everyone knows what I mean. If I say that Bob and Frank are married, everyone knows what that means, too. Some folks might say that Bob and Frank shouldn’t be married, or that in the eyes of God or of the government they aren’t married and that my statement is therefore incorrect, but it’s still clear what it means to say that they are married.
Compare this to other words: If I say that a table is orange, you’ll understand me (though, again, you might think that the table shouldn’t be orange), but if I say that gravity is orange, you would ask me what in the world it means for gravity to be orange, and that I’m not making sense. From this we see that the word “orange” encompasses things like tables, but does not encompass things like gravity. If someone tried to pass a law permitting orange gravity, I’d oppose that law because it was ridiculous.
In short, the purpose of words is to communicate, and a word that successfully communicates something is a valid use of that word. “Same-sex marriage”, or the word “marriage” used in a same-sex context, clearly communicates, whereas “orange gravity” does not. Therefore, even though some words can’t be sensibly applied to some situations, “marriage” as applied to same-sex unions is not one of them.