1. [U] a kind or forgiving attitude towards sb that you have the power to harm or right to punish humanity: to ask / beg / plead for mercy They showed no mercy to their hostages. God have mercy on us. The troops are on a mercy mission (= a journey to help people) in the war zone. 2. [C, usually sing.] (informal) an event or a situation to be grateful for, usually because it stops sth unpleasant: It’s a mercy she wasn’t seriously hurt. His death was a mercy (= because he was in great pain.