Mug1  —n. 1 a drinking-vessel, usu. Cylindrical with a handle and no saucer. B its contents. 2 slang gullible person. 3 slang face or mouth. —v. (-gg-) attack and rob, esp. In public.  a mug's game colloq. Foolish or unprofitable activity.  mugger n. Mugful n. (pl. -s). Mugging n. [scandinavian]