A Mackintosh is a form of waterproof raincoat[?], first sold in 1824, made out of rubberized fabric. The Mackintosh is named after its Scottish inventor Charles Macintosh: note the added letter 'k' in the name of the garment.
As well as their practical use as a rainproof garment, Mackintoshes feature in a peculiarly British form of rubber fetishism.