Noun. An assemblage of demons.

Slavery..unless it had been now and then checked, would have transformed the earth ere now into a demonagerie.
Tait’s Edinburgh Magazine, XV p 433 – 1848 

Demon + Menagerie. Pretty good combo! Good enough to catch my eye at least. I don’t know how often this one might come up in general conversation but when the opportunity presents itself — USE IT! You will impress your friends and foes alike.

The word conjures a great image in my head of hellish beasts lined up neatly ready to smite something with their smiteful powers.

It might find its way into the vocabularies of religious or political leaders inspiring fear into the hearts of the masses, warning of the price to pay for sinning, and the impending armageddon.

Not to be confused with a demonage a trois: something to be avoided.