The Sicemonite Sector was an astro-geographical region that was composed of the Sise System, Rettna, Lexrul, Deysum, Ubrikkia and Uogo'cor. It also had jurisdiction over a large portion of empty space next to those systems. It bordered the Ootmian Pabol and Trax Tube, which intersected the Bothan Run and Gamor Run hyperspace routes. It bordered the Halla sector, Hutt Space and the Mytaranor sector. The Sicemonite Sector was located near Boz Pity, Kashyyyk and Lannik. In 66 BBY the sector had its name changed.
Sicemonite Sector officially changed its name in 66 BBY to incorporate an uppercase spelling of sector, despite rules by the Republic to the contrary. The Emperor felt that the Sicemonite region was "exceptional and should not conform the to the Republic's insistence on uniformity." They also cited the 490 BBY petition by the Corporate Sector as a precedent to their cause. Their lobbying was successful, and the name was change from Sicemonite sector, to Sicemonite Sector.
Behind the scenes
The Sicemonite Sector is capitalized in-universe because of the deliberately portrayed arrogance of the Sicemonite Emperor and father of Mason Quarrell. This was supposed to flesh out the Emperor's arrogance (which pushes away Mason) and to create something unique for this sector.