What was a raincoat before it was a "slicker?" A mac. The mackintosh raincoat bears the name of its inventor, Scotsman Charles Macintosh, an enterprising clerk-turned-chemist (1766-1843) who invented the process of weatherproofing and produced a practical cloth. The mac was made with double-thick fabric and a middle layer of rubber. It became popular overnight. Mackintosh should be macintosh, but the incorrect spelling prevails. Nonetheless, Macintosh revolutionized outdoor living. His waterproof fabric was used for life preservers, fishing boots, camping gear, and hot-water bottles.
Most cultures have had to deal with the problem of wet feet. The solution? Overshoes. In France, they are galoche, in Spain and Portugal, galocha, in Italy galoscia, and in ancient Greece, kalopous. In the days when shoes were made of fine cloth, galoshes were wooden sandals fastened to the feet with leather thongs. The word galoshe means "shoemaker's last" or "wooden foot." These wooden clogs became today's rubber overshoes.
SOURCES: Morris Dictionary of Word and Phrase Origins by W. and M. Morris, The Encyclopedia of Word and Phrase Origins by Robert Hendrickson.