devil (n.)

c. 1200, "an evil spirit, malignant supernatural being, an incubus, a devil," from Latin daemon "spirit," from Greek daimōn "deity, divine power; lesser god; guiding spirit, tutelary deity" (sometimes including souls of the dead); "one's genius, lot, or fortune;" from PIE *dai-mon- "divider, provider" (of fortunes or destinies), from root *da- "to divide."

The malignant sense is because the Greek word was used (with daimonion) in Christian Greek translations and the Vulgate for "god of the heathen, heathen idol" and also for "unclean spirit." Jewish authors earlier had employed the Greek word in this sense, using it to render shedim "lords, idols" in the Septuagint, and Matthew viii.31 has daimones, translated as deofol in Old English, feend or deuil in Middle English. Another Old English word for this was hellcniht, literally "hell-knight."

The usual ancient Greek sense, "supernatural agent or intelligence lower than a god, ministering spirit" is attested in English from 1560s and is sometimes written daemon or daimon for purposes of distinction. Meaning "destructive or hideous person" is from 1610s; as "an evil agency personified" (rum, etc.) from 1712.

The Demon of Socrates (late 14c. in English) was a daimonion, a "divine principle or inward oracle." His accusers, and later the Church Fathers, however, represented this otherwise. The Demon Star (1895) is Algol (q.v.) .

proper name of the supreme evil spirit and great adversary of humanity in Christianity, Old English Satan, from Late Latin Satan (in Vulgate in the Old Testament only), from Greek Satanas, from Hebrew satan "adversary, one who plots against another," from satan "to show enmity to, oppose, plot against," from root s-t-n "one who opposes, obstructs, or acts as an adversary."

In the Septuagint usually translated into Greek as diabolos "slanderer," literally "one who throws (something) across" the path of another (see devil (n.)), though epiboulos "plotter" is once used.

In biblical sources the Hebrew term the satan describes an adversarial role. It is not the name of a particular character. Although Hebrew storytellers as early as the sixth century B.C.E. occasionally introduced a supernatural character whom they called the satan, what they meant was any one of the angels sent by God for the specific purpose of blocking or obstructing human activity. [Elaine Pagels, "The Origin of Satan," 1995]

In Middle English also Satanas, Sathanas.