1N-COUNT （尤指特殊防水材料制成的）雨衣 A mac is a raincoat, especially one made from a particular kind of waterproof cloth. （尤指特殊防水材料制成的）雨衣 [British]
2N-VOC (常用作称呼不知姓名的男子)老兄，老弟Mac is sometimes used, mainly by men, as a term of address for a man whose name they do not know. (常用作称呼不知姓名的男子)老兄，老弟 [US, informal]