fabulous

First recorded in 1540–50; from Latin fābulōsus, equivalent to fābul(a) “a story, tale” + -ōsus adjective suffix; see fable, -ous

The core meanings of fabulous are perfect reflections of their Latin roots, which point directly to the word fable. Fables are creative tales or legends, often with magical creatures or great adventures. So when we talk about someone making up a fabulous excuse (which is “almost impossible to believe”) or we read about a fabulous winged horse (which is “purely imaginary”), we are staying pretty close to the Latin origin.
But in everyday usage, the most familiar sense of fabulous may be the informal one—“exceptionally good, wonderful”—which strays from the direct line to fable. Such remarks as “What a fabulous meal!” or “How’s that fabulous brother of yours?” are so common that it would not occur to us to stop and think, “Hey, did he just accuse me of preparing imaginary food?” or “Hmm, does she think my brother is a superhero, or that he’s just not very believable?”
Some might say that the only drawback to such familiarity with fabulous’s informal meaning is that we sometimes have to stop and think when it’s being used as originally intended. If I told you I just read a fabulous tale, could you be sure what I meant by that?

C15: from Latin fābulōsus celebrated in fable, from fābula fable