No, it's not the name of a disinfectant used by exorcists, but rather the title of Lucio Fulci's 1989 film about demonic possession on the island of Sicily.
Brett Halsey and Meg Register star as a pair of archeologists, one sensible and scientific, the other sensitive and superstitious, whose latest dig is plagued by a series of violent, non-Mafia-related deaths. It seems a local Medieval nunnery was once the site of devil worship, flagrant carnality and ritualistic murder - until the locals banded together to exorcise the evil by crucifying the nuns (depicted in the film's prologue). Turning a deaf ear to the warnings of the village leader and the local butcher, the archeologists carry on digging, and ultimately loosing the hounds of Hell, Fulci-style.
DEMONIA is a largely uninteresting affair, sluggishly paced and directed with apparent indifference by Fulci. Everything seems a bit tame (artfully placed blankets throw cold water on the orgy scenes) and second hand, from Giovanni Cristiani's corny, tympani-heavy score to the use of such hoary spook-cinema devices as double exposures to suggest ghostly apparitions and echoey dream voices (has anyone in your dreams ever spoken with an echoey voice?). Fulci stumbles further by having his heroine plagued by nightmares that offer no information beyond what we already saw in the prologue.
Fulci himself turns up late in the film as an inspector from Scotland Yard, only to turn up clues to a mystery that is no mystery to us; worse yet, Fulci's Inspector Carter's last scene finds him eyeballing a piece of cloth (torn from the habit of one of the murderous ghost-nuns), identifying it as centuries old, and then disappearing from the film entirely). Al Cliver (aka Pier Luigi Conti) appears as Porter, a fellow archeologist who meets an untimely end at the hands of a transparent, headless, speargun-toting haint (Fulci regular Cliver is billed in the credits as Al "Clever").
The film perks up a bit halfway through, when the local medium (a character similar to one played by Rada Rassimov in Mario Bava's BARON BLOOD) meets her predetermined demise by dint of half a dozen cat hand puppets, but DEMONIA is still slow going. A third act disemboweling of one of the dig members is gross but unconvincing, and the film climaxes on an ambiguous note that fails to satisfy or justify the investment of an hour and a half.
