I'm not confused--I was just surprised in reading definition #3.

And I've figured out why I would have assumed incorrectly that a "ponderous speech" would have been a "well-thought-out" one:

I would have considered the word "ponder"--to think deeply. And then I would have leapt to the conclusion that a ponderous speech would have been one that had been deeply thought out. I would never have considered--prior to reading definition #3--that the speech was walking along on too-heavy, dull legs.

The only reason I raised the topic here was to see whether there were any of us out there who would have made the same error as I had made. I think it's interesting to come across assumptions we make about words and suddenly one day to realize that our assumption had been incorrect. Wrong root; wrong word; wrong usage.

Best regards,
WrongWord