The ultimate f-word

I stumbled upon it by accident. It's a word unlike any other and orders of magnitude more powerful than any f-word you've thought of all ready. The amazing thing is it's a word you know.But this word is like a gun. We know what a gun is, and some of us have handled and fired them. But the vast-vast majority of us have never used a gun to terrify someone. But you know a word that can terrify a