Bailiwick is an old legal term from England, a compound of bailie + -wick. Bailie is an obsolete form of bailiff, an administrative official, from the Middle English and Old French bailli; -wick is from the Old English wic, meaning dwelling, farm, town, or enclosed space.
The term bailiwick dates to the mid-15th century and originally meant the district under a bailiff’s jurisdiction. The legal sense meaning a jurisdiction is still current. The term was brought to America in the mid-19th century, where it generalized to mean a person’s sphere of knowledge or expertise.
(Source: Oxford English Dictionary, 2nd Edition)
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