Because I know people use big words, but they really mean short things.

What's gone on in the media these past six months doesn't mean a thing.

Just because you have brown hair and eyes doesn't mean a thing.

Put them all together and they don't mean a thing.

As you can see, these terms do not mean the same thing.

Maybe not in my words, but they mean the same thing.

Often the two terms are used to mean the same thing.

But when people say these words, they usually mean the same thing.

Why have different words if they all mean the same thing?

They mean not quite the same thing, but they're in relationship with each other.