Turn King’s/Queen’s evidence
Definition 1 of 1
Pro Tip 1/3Legal Jargon
The phrase is commonly used in legal contexts and might not be understood outside of this domain. 
In court dramas, characters sometimes turn King's evidence for a reduced sentence.
Pro Tip 2/3Historical Origin
Originally UK-based, it refers to 'King' or 'Queen' depending on the reigning monarch. 
As she agreed to turn Queen's evidence, she felt like a character from a historical novel.
Pro Tip 3/3Deal Making
Implies a deal where someone gives up information in exchange for a lighter sentence or immunity. 
He negotiated to turn King's evidence and get out of jail time.