When I read the first part of Origin of Species, Darwin made predictions where, I thought, "oh, that's just genetics and DNA." (Of course, he didn't know at the time.)
In addition to your example, there has been a pretty continuous supply of "predictions" that Einstein made that later proved correct when experiments were run.
We speculate that something is true. We predict that our speculation will be confirmed through observation.
We speculate that there is gold in X location. We predict that gold will be found in X location.