traitor |ˈtrātər|
noun
a person who betrays a friend, country, principle, etc. : they see me as a traitor, a sellout to the enemy.

PHRASAL VERBS
turn traitor betray a group or person : to think of a man like you turning traitor to his class.

DERIVATIVES
traitorous |-tərəs| adjective
traitorously adverb

ORIGIN Middle English : from Old French traitour, from Latin traditor, from tradere ‘hand over.’