Lewis Short
firmÄtor (noun M) : firmo
* A confirmer, establisher (post-Aug. and very rare): missus Drusus paci firmator (so acc. to Cod. Med., not pacis),Tac. A. 2, 46: disciplinae militaris,Plin. Ep. 10, 38, 1.
Charlton T. Lewis, Charles Short, A Latin Dictionary