Definitions of betray:

• verb:   deliver to an enemy by treachery

  Example: "The spy betrayed his country"

• verb:   reveal unintentionally

  Example: "Her smile betrayed her true feelings"

• verb:   cause someone to believe an untruth
• verb:   disappoint, prove undependable to; abandon, forsake
• verb:   give away information about somebody
• verb:   be sexually unfaithful to one's partner in marriage