Pandemonium was coined by Milton in his 1667 Paradise Lost:
A solemn Councel forthwith to be held At Pandæmonium, the high Capital Of Satan and his Peers.
To get the word, Milton combined a couple of Greek roots, pan meaning all + demon, with the Latin -ium ending. So pandemonium is literally the place of all demons. While pandemonium is a relatively modern invention, the word demonium, meaning abode of demons or hell, did exist in classical Latin.
Within a century or so, the word was being used in extended senses, referring to things akin to a real hell and eventually to the modern meaning of confusion, tumult, or uproar. From the 1755 M—cki—n’s Answer to Tully:
As I had at the Beginning...waggishly term’d the Audience my Pandemonium; a Hiss was the most proper Token of Applause.
The term does not derive, as is often thought, from the name of the Greek god Pan. Nor does its origin have anything to do with the excitement over the arrival of Pandas at the National Zoo in Washington in the 1970s (although I’m sure many journalistic wags overused the term “pandamonium” in describing this event).
(Source: Oxford English Dictionary, 3rd Edition)
Copyright 1997-2015, by David Wilton