a dishonest person (especially when playing games)

person who fools others

a person who cooperates with the enemy

traitor

an animal like, but larger than, a mouse; a person who deserts a cause that he or she thinks is about to fail

informer

to steal (something of little or no value); to report (about a person) to an official

informer

a person who gives advice about who will win races

informer

a person who betrays a friend, is disloyal to his country etc

person who is disloyal

a person who leaves one group and joins another

traitor

a kind of small, fierce animal with red-brown fur

sneak