An informal British nickname for the pop musician Paul McCartney, especially in tabloid newspapers — the loud, gossipy papers that like short, matey names in headlines. It sounds as if everyone already knows him. Though actually, this is in-group British pop talk, not a formal name, and not how you should write him in a school essay. The same spelling can mean other people called Mac, and in Australia Macca’s often means McDonald’s; those are different uses. This sense is the McCartney one.