"armies, hosts," only in Scripture, "the heavenly hosts," used as part of a title of God (Lord of Sabaoth), early 14c., from Late Latin Sabaoth (pl.), from Greek Sabaoth, transliterating Hebrew tzebhaoth "hosts, armies," plural of tzabha "army," from tzaba "he waged war, he served."

The word was translated in English in the Old Testament by the phrase "Lord of Hosts," but left untranslated in the New Testament (and in the "Te Deum") in Lord of Sabaoth. It sometimes is confused with unrelated Sabbath.

"witches' sabbath," a midnight meeting supposed to have been held annually by demons, sorcerers, and witches under the leadership of Satan, to celebrate their orgies, 1650s, a special application of the French form of Sabbath (q.v.).

"pertaining to the Sabbath or its observance," 1630s, from Latin sabbatarius (adj.), from sabbatum (see Sabbath).

also sometimes Sabbatharian, 1610s, "a Christian or Jew unusually strict about Sabbath observation," from Latin sabbatarius (adj.), from sabbatum (see Sabbath). Especially of members of Christian sects which maintained the Sabbath should be observed on the seventh day of the week (and not the first) is from 1640s; earlier sabbatary (1590s). It took on tones of reproach when used of Puritans deemed overzealous to interdict worldly pastimes and recreations on the Sabbath.

Not to be confused with Sabbatian (n.) "member of a sect founded by Sabbatus, a convert from Judaism "who seceded from the Novatianists before 380, having adopted Quartodeciman views" [OED]. Related: Sabbatartianism. Sabbatism is used in the general sense of "observance of the Sabbath or a sabbath as a day of rest from labor" (from Late Latin sabbatismus, from Greek sabbatismos).

1590s, "recurring in sevens or on every seventh;" 1640s, "of or suitable for the Sabbath," from Latin sabbaticus, from Greek sabbatikos "of the Sabbath," from sabbaton (see Sabbath). By 1836 as "characterized by rest or cessation from labor or tillage." Other adjectives from Sabbath include Sabbatary, Sabbatine.

 The noun meaning "a year's absence granted to researchers" (originally one year in seven, to university professors) is from 1934, short for sabbatical year, etc., which was recorded by 1886 (the thing itself is attested from 1880, at Harvard), a term perhaps suggested by the sabbatical year (1590s) in Mosaic law, the seventh year, in which land was to remain untilled and non-foreign debtors and slaves released.

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).

1934, from Hebrew shabbat (see Sabbath). Earlier in English as Shabbos (1870), from Yiddish shabes. Hence the salutation Shabbat shalom "a peaceful sabbath."