1. a person who secretly enters or joins a group, organization, or place in order to gather information or cause damage

Examples

• The security team discovered an infiltrator in their ranks.
• Police suspected that an infiltrator had leaked information to the press.
• The rebel group was careful to screen new members for potential infiltrators.
• An enemy infiltrator was caught trying to access classified documents.
• The company hired security experts to identify any infiltrators among their employees.
• The infiltrator had been gathering intelligence for months before being discovered.