/ˈtreɪtə(r) ||; ˈtretɚ/noun [C]
a traitor (to sb/sth) a person who is not loyal to his/her country, friends, etc 叛徒；卖国贼
A traitor betrays his/her friends, country, etc and the crime against his/her country is called treason. 叛徒出卖(betray)朋友、国家等。叛国罪叫做treason。