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).

1590s, "time of merrymaking," from Latin Saturnalia, the ancient Roman festivals of Saturn (held in December), a time of feasting and mirthful license for all classes, even slaves; neuter plural of the adjective Saturnalis "pertaining to Saturn," from Saturnus (see Saturn). They correspond to the Greek Kronia.

The extended sense of "period of wild or noisy revelry" is attested by 1782. Related: Saturnalian.

1550s, "pertaining to the planet Saturn;" 1610s, "pertaining to the god Saturn or his reign," from French saturnien, from Latin saturnius, from Saturn (see Saturn).

As a noun, 1590s as "one born under the influence of Saturn;" by 1738 as "a native or inhabitant of Saturn."

Some cold Saturnian, when the lifted tube

Shows to his wond'ring eye our pensile globe,

Pities our thirsty soil, and sultry air,

And thanks the friendly pow'r that fix'd him there.

[Richard Savage, "The Genius of Liberty," dated 1734, published in Gentleman's Magazine, June 1738]

"gloomy, morose, sluggish, grave, not readily made excited or cheerful," mid-15c., literally "born under the influence of the planet Saturn," from Middle English Saturne (see Saturn) + -ine (1). Old medicine believed these characteristics to be caused or influenced by the astrological influence of the planet Saturn, which was the most remote from the Sun (in the knowledge of the times) and thus coldest and slowest in its revolution. Saturn also was associated alchemically with lead.