fiefdom

a region of activity, knowledge, or influence you'll have to ask that guy—the project is his fiefdom Synonyms area, arena, bailiwick, barony, business, circle, demesne, department, discipline, domain, element, fief, field, firmament, front, game, kingdom, line, precinct, province, realm, specialty, sphere, terrain, walkRelated Words frontier; study, subject; territory, turf; occupation, profession, pursuit, racket, vocation; ambit, amplitude, breadth, compass, confine, dimension(s), extent, ken, reach, scope, sweep, width; subfield, subspecialty