O.E. sabat "Saturday," observed by the Jews as a day of rest,
from L. sabbatum, from Gk. sabbaton, from Heb. shabbath, prop. "day of rest," from shabath "he rested."
The Babylonians regarded seventh days as unlucky, and avoided certain activities then; the Jewish observance may have begun as a similar custom.
From the seventh day of the week, it began to be applied early 15c. to the first day (Sunday), a change completed during the Reformation.
The original meaning is preserved in Sp. Sabado, It. Sabbato, and other languages' names for "Saturday." Hung. szombat, Rumanian simbata, Fr. samedi, Ger. Samstag "Saturday" are from V.L. sambatum, from Gk. *sambaton, a vulgar nasalized variant of sabbaton.