Mac n 1 (abbr. of “Macintosh”) a light waterproof jacket which can usually be squashed up into an impressively small size for packing away. Possibly derived from the name of the gentleman who worked out how to infuse rubber and cloth. Americans call the same sort of thing a “slicker.” 2 something along the lines of “mate.” The two meanings appear together in the Bonzo Dog Doodah Band's song “Big Shot”, which features the lines: “On the way home a punk stopped me: “You got a light, mac?” / I said “No, but I've got a dark brown overcoat.”