sabbatical year

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A leave of absence, often with pay, usually granted every seventh year, as to a college professor, for travel, research, or rest.
2. n. A year during which land remained fallow, observed every seven years by the ancient Jews.

Wiktionary

1. n. A year of rest for the land observed every seven years in ancient Judea, which included allowing the fields to lie without tilling, sowing, or reaping from one autumn to the next in accordance with a Levitical commandment.
2. n. A leave, often with full or half pay granted (as every seventh year) to one holding an administrative or professional position for rest, travel, or research.

GNU Webster's 1913

1. adj. (Jewish Antiq.) every seventh year, in which the Israelites were commanded to suffer their fields and vineyards to rest, or lie without tillage.

WordNet 3.0

1. n. a sabbatical leave lasting one year