bailiwick \BAY-luh-wik\ (noun) - 1 : A person's specific area of knowledge, authority, interest, skill, or work. 2 : The office or district of a bailiff.
"I'm all of that, Skye. I'm also King. This is my bailiwick. My word is law and my fists enforce it." -- Richard S. Wheeler, 'Rendezvous'
Bailiwick comes from Middle English baillifwik, from baillif, "bailiff" (ultimately from Latin bajulus, "porter, carrier") + wik, "town," from Old English wic, from Latin vicus, "village."