Source : Webster's Revised Unabridged Dictionary (1913)

Treasonous \Trea"son*ous\, a.
   Treasonable. --Shak.

         The treasonous book of the Court of King James.
                                                  --Pepys.

Source : WordNet®

treasonous
     adj : constituting treason; "a traitorous act"; "treasonable acts
           like sabotage" [syn: {traitorous}, {treasonable}]