area, arena, bailiwick, barony, business, circle, demesne, department, discipline, domain, element, fief, fiefdom, field, firmament, front, game, line, precinct, province, realm, specialty, sphere, terrain, walk

frontierstudy, subjectterritory, turfoccupation, profession, pursuit, racket, vocationambit, amplitude, breadth, compass, confine, dimension(s), extent, ken, reach, scope, sweep, widthsubfield, subspecialty