/ ˈtreɪtə(r); NAmE / noun
traitor (to sb/sth) a person who gives away secrets about their friends, their country, etc. :
He was seen as a traitor to the socialist cause.
She denied that she had turned traitor (= become a traitor ) .
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WORD ORIGIN
Middle English : from Old French traitour , from Latin traditor , from tradere hand over.