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demon (n.)[demon 词源字典]: c. 1200, from Latin daemon "spirit," from Greek daimon "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" (see tide (n.)).

Used (with daimonion) in Christian Greek translations and Vulgate for "god of the heathen" and "unclean spirit." Jewish authors earlier had employed the Greek word in this sense, using it to render shedim "lords, idols" in the Septuagint, and Matt. 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 original mythological sense is sometimes written daemon for purposes of distinction. The Demon of Socrates 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.[demon etymology, demon origin, 英语词源]
devil (n.): Old English deofol "evil spirit, a devil, the devil, false god, diabolical person," from Late Latin diabolus (also the source of Italian diavolo, French diable, Spanish diablo; German Teufel is Old High German tiufal, from Latin via Gothic diabaulus).

The Late Latin word is from Ecclesiastical Greek diabolos, in Jewish and Christian use, "Devil, Satan" (scriptural loan-translation of Hebrew satan), in general use "accuser, slanderer," from diaballein "to slander, attack," literally "throw across," from dia- "across, through" + ballein "to throw" (see ballistics). Jerome re-introduced Satan in Latin bibles, and English translators have used both in different measures.

In Vulgate, as in Greek, diabolus and dæmon (see demon) were distinct, but they have merged in English and other Germanic languages.

Playful use for "clever rogue" is from c. 1600. Meaning "sand spout, dust storm" is from 1835. In U.S. place names, the word often represents a native word such as Algonquian manito, more properly "spirit, god." Phrase a devil way (c. 1300) was originally "Hell-ward, to Hell," but by late 14c. as an expression of irritation.

Devil's books "playing cards" is from 1729, but the cited quote says they've been called that "time out of mind" (the four of clubs is the devil's bedposts); devil's coach-horse is from 1840, the large rove-beetle, which is defiant when disturbed. "Talk of the Devil, and he's presently at your elbow" [1660s].
prevaricator (n.): c. 1400, from Old French prevaricator and directly from Latin praevaricator "sham accuser; unfaithful advocate," agent noun from past participle stem of praevaricari (see prevaricate).
sycophant (n.): 1530s (in Latin form sycophanta), "informer, talebearer, slanderer," from Middle French sycophante and directly from Latin sycophanta, from Greek sykophantes "false accuser, slanderer," literally "one who shows the fig," from sykon "fig" (see fig) + phainein "to show" (see phantasm). "Showing the fig" was a vulgar gesture made by sticking the thumb between two fingers, a display which vaguely resembles a fig, itself symbolic of a vagina (sykon also meant "vulva"). The modern accepted explanation is that prominent politicians in ancient Greece held aloof from such inflammatory gestures, but privately urged their followers to taunt their opponents. The sense of "mean, servile flatterer" is first recorded in English 1570s.
The explanation, long current, that it orig. meant an informer against the unlawful exportation of figs cannot be substantiated. [OED]
accusant: "A person who accuses; an accuser", Late Middle English; earliest use found in Guy de Chauliac's Grande Chirurgie. Partly from Middle French, French accusant (noun) person who accuses, (adjective) that accuses, and partly from classical Latin accūsant-, accūsāns, present participle of accusāre accuse.