Weaponmaster is a title that is granted by the Mantis , to those of Mantis bloodline who have proven their absolute skill and mastery of their weapon of choice.
In the Lowlands this honour is bestowed by visiting the barely inhabited and forested island of Parasyol. There, the supplicant engages in a ritual involving something like a vision quest, visiting a shrine and confronting an actual Mantis (or possibly the Ancestor Form?). Those that survive find they have somehow acquired the golden badge of a Weaponmaster. Presumably other areas have their own holy places, since the title also exists in the Commonweal .
All Weaponmasters are deadly in combat and have somehow developed the ability to summon their weapon to their hand from wherever it may be.