bailiwick

n. bailiff's jurisdiction (Law); person's area of authority; field of knowledge of a person, expertise of a person

A bailiwick is the area of jurisdiction of a bailiff. The term was also applied to a territory in which the sheriff's functions were exercised by a privately appointed bailiff under a Crown grant. The word is now more generally used in a metaphorical sense, to indicate a sphere of authority, experience, activity, study, or interest.
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Noun
1. the area over which a bailiff has jurisdiction
(hypernym) jurisdiction
2. a branch of knowledge; "in what discipline is his doctorate?"; "teachers should be well trained in their subject"; "anthropology is the study of human beings"
(synonym) discipline, subject, subject area, subject field, field, field of study, study, branch of knowledge
(hypernym) knowledge domain, knowledge base
(hyponym) occultism

(n.)
The precincts within which a bailiff has jurisdiction; the limits of a bailiff's authority.
  

The area of responsibility for a sheriff , responsible for keeping the peace and for enforcing the royal laws.