Stunning

I actually heard “flibbertigibbet”(twice) in a movie a few days ago! It was a very strange movie with Meg Ryan and Tom Hanks, called “Joe and the Volcano.”
A flibbertigibbet is an irresponsible, scatterbrained, or garrulous person. Remember to pronounce the G like J in jam. I’m not surprised that no etymology is given.

I found Flabberghast in my HUD huge unabridged dictionary. They list it as a combination of flabby (loose) and aghast (stunned or horrified). Aghast comes from Old English from a word that means ghost!

I'm astonished that we have so many words that mean stunned like aghast and flabbergasted.