ETYM Old Eng. traitour, Old Fren. traďtor, traďteur, French treître, Latin traditor, from tradere, traditum, to deliver, to give up or surrender treacherously, to betray; trans across, over + dare to give. Related to Date time, and cf. Betray,Tradition, Traditor, Treason.
Someone who betrays his country by committing treason; SYN. treasonist.