Etymology of demon (n.)

Around 1200 CE, the meaning of the word demon as "an evil spirit, malignant supernatural being, an incubus, a devil" started to emerge out of the Latin daemon, meaning "spirit." The Latin evolved from the Greek, which itself evolved from the Proto-Indo-European.

• From the Greek daimōn, meaning "deity or divine power; lesser god; guiding spirit or tutelary deity (sometimes including souls of the dead)"
• From the PIE dai-mon-, meaning "one's genius, lot or fortune"
• From the PIE root da-, meaning "divider or provider (of fortunes or destinies)"

The word took on a malignant sense because the Greek daimōn and daimonion were used in Christian Greek translations and the Vulgate for "god of the heathen; heathen idol; unclean spirit." Jewish authors had previously employed the Greek word in this sense, using it as a translation for shedim, meanining "lords; idols."

In the Septuagint, Matthew 8:31 contains daimones, translated as deofol in Old English, and as feend or deuil in Middle English. Another Old English word for this was hellcniht, meaning "knight of hell," or more literally, "hell-knight."

The usual ancient Greek sense, i.e. "supernatural agent or intelligence lower than a god; ministering spirit," is attested in English from the 1560s onward and is sometimes written as daemon or daimōn for purposes of distinction (i.e. Latin vs. Greek). The ideas of demons being "destructive or hideous persons" or "evil agencies personified" emerged around the 1610s and 1710s, respectively.