1. in a manner that violates allegiance, duty, or faith to a person, group, or cause

Examples

• He disloyally revealed his friend's secret to their rival.
• The employee disloyally shared confidential company information with a competitor.
• She acted disloyally by supporting the opposing team despite her family's long tradition.
• The general disloyally conspired against the king during the war.
• He disloyally abandoned his teammates when they needed him most.