turn one's coat

present singular third person turns one's coat · participle present turning one's coat · participle past turned one's coat · past turned one's coat · alternative turn coat

1. idiomaticTo turn against a previous affiliation or allegiance.

   Bruce would scarcely have found this sufficient cause to turn his coat.

   2012, Nigel Tranter, The Wallace, →ISBN

   2 more examples

   To meet the exigence of the moment, a considerable army was raised under General Baillie, a Presbyterian officer of skill and fidelity, with whom was joined in command the celebrated Sir John Urrie, a soldier of fortune like Dalgetty, who had already changed sides twice during the Civil War, and was destined to turn his coat a third time before it was ended.

   1819, Sir Walter Scott, A Legend of Montrose

   He also knew that here, in Connecticut, the chance of finding rebels who would turn their coats was far greater than it was in Boston which, for over two years now, had been the epicenter of the unrest that threatened peace with Britain.

   2014, Scott Stanley, Betrayal of the Cloak, →ISBN, page 44

2. Used other than figuratively or idiomatically: see turn, coat.

   Synonyms: change sides, defect