Shadesworn was the name all Dajorran natives gave to their Force-using masters. Every member of Clan Arcona, by right, are Shadesworn as they are members of the Shadow Clan.
Only a select few earn the title of 'True' Shadesworn, though. To become a True Shadesworn, a member must be of either the Obelisk Assassin discipline, or have met and exceeded other expectations set forth by the Shadow Lord. True Shadesworn are the best assassins in the galaxy, so much so that their target's are labeled as 'deaders' because a True Shadesworn never misses his mark.