In Scripture and in Catholic theology this word has come to mean much the same as devil and denotes one of the evil spirits or fallen angels. And in fact in some places in the New Testament where the Vulgate, in agreement with the Greek, has daemonium, our vernacular versions read devil. The precise distinction between the two terms in ecclesiastical usage may be seen in the phrase used in the decree of the Fourth Lateran Council. "Diabolus enim et alii daemones" (The devil and the other demons), i.e. all are demons, and the chief of the demons is called the devil. This distinction is observed in the Vulgate New Testament, where diabolus represents the Greek diabolos and in almost every instance refers to Satan himself, while his subordinate angels are described, in accordance with the Greek, as daemones or daemonia This must not be taken, however, to indicate a difference of nature; for Satan is clearly included among the daemones in James 2:19 and in Luke 11:15-18. But though the word demon is now practically restricted to this sinister sense, it was otherwise with the earlier usage of the Greek writers. The word, which is apparently derived from daio "to divide" or "apportion", originally meant a divine being; it was occasionally applied to the higher gods and goddesses, but was more generally used to denote spiritual beings of a lower order coming between gods and men. For the most part these were beneficent beings, and their office was somewhat analogous to that of the angels in Christian theology. Thus the adjective eydaimon "happy", properly meant one who was guided and guarded by a good demon. Some of these Greek demons, however, were evil and malignant. Hence we have the counterpart to eudamonia "happiness", in kakodaimonia which denoted misfortune, or in its more original meaning, being under the possession of an evil demon. In the Greek of the New Testament and in the language of the early Fathers, the word was already restricted to the sinister sense, which was natural enough, now that even the higher gods of the Greeks had come to be regarded as devils.

We have a curious instance of the confusion caused by the ambiguity and variations in the meaning of the word, in the case of the celebrated "Daemon" of Socrates. This has been understood in a bad sense by some Christian writers who have made it a matter of reproach that the great Greek philosopher was accompanied and prompted by a demon. But, as Cardinal Manning clearly shows in his paper on the subject, the word here has a very different meaning. He points to the fact that both Plato and Xenophon use the form daimonion, which Cicero rightly renders as divinum aliguid, "something divine". And after a close examination of the account of the matter given by Socrates himself in the reports transmitted by his disciples, he concludes that the promptings of the "Daemon" were the dictates of conscience, which is the voice of God.

It may be observed that a similar change and deterioration of meaning has taken place in the Iranian languages in the case of the word daeva. Etymologically this is identical with the Sanskrit deva, by which it is rendered in Neriosengh's version of the Avesta. But whereas the devas of Indian theology are good and beneficent gods, the daevas of the Avesta are hateful spirits of evil

Beelzebub, or Baalzebûb, the Philistine god of Accaron (Ekron), scarcely 25 miles west of Jerusalem, whose oracle King Ochozias (Ahaziah) attempted to consult in his last illness, IV (II) Kings, i, 2. It is only as an oracle that the god is known to us; no other mention of him occurs in the Old Testament. The name is commonly translated "the lord of the flies", and the god is supposed to be so called either because as a sun god he brings the flies, though the Ba'al was probably not a sun god, or more likely because he is invoked to drive away the flies from the sacrifice, like the Zeus Apomuios, who drove them from Olympia, or the hero Myiagros in Arcadia. Halévy and Winckler interpret the name, according to the analogy of very many names compounded with baal, as "the lord of Zebub", supposed to be a locality in Accaron; there is no proof, however, for the existence of such a locality, and besides Beelzebub is called the god of Accaron. Cheyne thinks the original form of the name is Ba'al Zebul, "the lord of the mansion," or high house, which would refer to the god's temple or to the mountain on which the gods dwelt, or rather, in his opinion, to both. But the textual evidence, as Lagrange objects, is entirely in favour of Zebub. Cheyne, admitting this, holds that the title "lord of the high house", which would suggest to the writer of Kings a reference to Yahweh's temple or to His heavenly dwelling place, would be considered offensive, and would induce him, in contempt, to change it to Ba'al Zebub, the lord of flies. The tradition of the true name, lingering on, accounts for its presence in the Gospels (Zeboul). This conjecture, which has a certain plausibility, leaves unexplained why the contempt should lead to the particular form, Baal Zebub, a name without parallel in Semitic religions. It seems more reasonable, then, to regard Baalzebub as the original form and to interpret it as "lord of the Flies".