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.
updated on October 31, 2021