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.
seventh or last day of the week, Old English sæterdæg, sæternesdæg, literally "day of the planet Saturn," from Sæternes (genitive of Sætern; see Saturn) + Old English dæg (see day). Partial loan-translation of Latin Saturni dies "Saturn's day" (compare Dutch Zaterdag, Old Frisian Saterdi, Middle Low German Satersdach; Irish dia Sathuirn, Welsh dydd Sadwrn). The Latin word itself is a loan-translation of Greek kronou hēmera, literally "the day of Cronus."
German Samstag (Old High German sambaztag) appears to be from a Greek *sambaton, a nasalized colloquial form of sabbaton "sabbath" (see Sabbath), which also yielded Old Church Slavonic sabota, Polish sobota, Russian subbota, Hungarian szombat, French samedi.
Unlike other English day names there was no Germanic substitution, perhaps because the northern European pantheon lacks a match to Roman Saturn. A homely ancient Nordic custom seems to be preserved in Old Norse day names laugardagr, Danish lørdag, Swedish lördag "Saturday," literally "bath day" (Old Norse laug "bath").
Saturday night has been figurative of revelry and especially "drunkenness and looseness in relations between the young men and young women" ["Clara Hopwood"] at least since 1847. Saturday-night special "cheap, low-caliber handgun" is American English, attested from 1976 (earlier Saturday-night pistol, 1929).
Old English Sætern, name of the Roman god, also, in astronomy, the name of the most remote planet (then known); from Latin Saturnus, originally a name of an Italic god of agriculture, possibly from Etruscan. Derivation from Latin serere (past participle satus) "to sow" is said to be folk-etymology.
An ancient Italic deity, popularly believed to have appeared in Italy in the reign of Janus, and to have instructed the people in agriculture, gardening, etc., thus elevating them from barbarism to social order and civilization. His reign was sung by the poets as "the golden age." [Century Dictionary]
Identified with Greek Kronos, father of Zeus. Also the alchemical name for lead (late 14c.). In Akkadian, the planet was kaiamanu, literally "constant, enduring," hence Hebrew kiyyun, Arabic and Persian kaiwan "Saturn."