† ˈtreasonful,a.Obs.rare. [f. treason n. + -ful.] Full of treason; treasonous; treacherous. 13..Cursor M. 13960 (Cott.) Þe Iues..wit þair mani tressunful red, þai soght ihesu at do to ded.1650Trapp Comm.Num. xvi. 14 They add rebellion to sin, and justifie their treasonful practices.