1expose (one’s country, a group, or a person) to danger by treacherously giving information to an enemy:a double agent who betrayed some 400 British and French agents to the Germans
treacherously reveal (information):many of those employed by diplomats betrayed secrets
be gravely disloyal to:the men who have betrayed British people’s trust
2unintentionally reveal; be evidence of:she drew a deep breath that betrayed her indignation
