why are terrible and horrible basically the same thing but horrific and terrific are basically the opposite

Question

English will never be something I fully understand

In: 9830

Answer 1

The old definition of terrific was to cause terror, but since it also can mean a large amount or something large or dense, it shares a definition with the word great. So it started being used interchangeably and the words definition evolved to include it meaning a great or good thing.