a. Pertaining to treason; consisting of treason; involving the crime of treason, or partaking of its guilt. [ 1913 Webster ]
Most men's heads had been intoxicated with imaginations of plots and treasonable practices. Clarendon. [ 1913 Webster ]
Syn. -- Treacherous; traitorous; perfidious; insidious. [ 1913 Webster ]
--Trea"son*a*ble*ness, n. -- Trea"son*a*bly, adv. [ 1913 Webster ]