Our word panic is a borrowing from Middle French panique, which, probably through Latin, goes back to the Greek word panikon. Panikon once did mean "sudden panic", but before that it carried the definition "of or pertaining to the god Pan", the deity-in-chief of the wild and shepherds. How did this change come about? Well, as a neat little side effect of being the god of the wild, Pan could create a primal scream which sent grown men reeling in absolute fear, according to legend of course. Now that you know that, let's go further. Panikon is a back-formation of the god's name, obviously, and Pan has cognates in the Indian languages that suggest a Proto-Indo-European root peh, which meant "protect" primarily, but also had the meaning of "shepherd", the one that evolved into Pan's name. Usage of the word panic has increased steadily since the 1980s, which does not bode well.
Adam Aleksic, a freshman studying linguistics at Harvard University, has been described as the internet's sixth most famous etymologist. He has disturbing interests in words, vexillology, geography, board games, limericks, and law, and he loves writing about himself in the third person.
The Etymology Nerd