Dæmon or daimôn are Latinized spellings of the Greek word δαίμων. It referes to the daemons of the ancient Greeks, which are good or benevolent spirits. In Plato's Symposium, the priestess Diotima teaches Socrates that "everything daemonic is between divine and mortal" (202d-e), and she describes daemons as "interpreting and transporting human things to the gods and divine things to men..." (202e).
The Hellenistic Greeks divided daemons into good and evil categories: agathodaimōn (αγαθοδαιμων "noble spirit"), from agathós (ἀγαθός: "good, brave, noble, moral, lucky, useful"), and kakódaimōn (κακοδαίμων: "malevolent spirit"), from kakós (κακός: "bad, evil").
German scholar of Greek mythology Walter Burkert suggests the Judeo-Christian use of demon in a strictly malignant sense begins in “the fifth century when a doctor asserts that neurotic women and girls can be driven to suicide by imaginary apparitions, ‘evil daimones’.” 
- Walter Burkert, Greek Religion (Cambridge, MA: Harvard University Press, 1985), 181.