A person who betrays their principles, allegiance, or side by switching to the opposite group, especially in politics or war.
From the practice of reversible coats worn in medieval and Renaissance times—soldiers could wear red on one side and blue on the other, literally flipping their coat to show allegiance to a different army. The term became figurative.
The most famous turncoat in American history is Benedict Arnold, whose betrayal during the Revolutionary War was so notorious that his name became synonymous with treason—but in the Civil War, many high-ranking military officers switched sides too, showing this happens constantly in human conflict.
Complete word intelligence in one call. Free tier — 50 lookups/day.