Queen’s evidence
noun/ˌkwiːnz ˈevɪdəns/
/ˌkwiːnz ˈevɪdəns/
[uncountable] (law)- (in the UK) if a criminal turns Queen’s evidence, they give evidence against the people who committed a crime with them ‘Queen's evidence’ is used when the United Kingdom has a queen, and ‘King’s evidence’ when it has a king.
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Queen’s evidence