Sabbatical \suh-BAT-i-kuhl\ , noun;
1. Any extended period of leave from one's customary work, especially for rest, to acquire new skills or training, etc.
1. Of or pertaining to or appropriate to the Sabbath
2. Bringing a period of rest
This word dates to the 1640's with the meaning "of or suitable for the Sabbath" from Latin sabbaticus, which is borrowed from Greek sabbatikos ("of the Sabbath"). Greek sabbaton ("Sabbath") comes from Hebrew shabbath ("day of rest") from shabath ("he rested"). The Babylonians considered the seventh day unlucky and avoided certain activities then, so it's likely that the Jewish custom was based on a similar custom. Obviously the Christian idea of the Sabbath comes from Judaism.
I have only heard this word being used by academics when they take a semester or a year off from their normal position to do research somewhere else. That type of sabbatical dates to the 1880's and it was originally something university professors would do for one year out of every seven in their career. The usage was invented by Harvard based on sabbatical year in Mosaic law, which states that every seventh year land is to be left unworked and debtors and slaves are released.
Today's word and the first definition were both taken from Dictionary.com's 'Word of the Day' for Friday, June 24
Etymologies come from the Oxford English Dictionary and/or Etymonline.com