Is it ensure, insure, or assure?
waterproof outer coat, 1836, named for Charles Macintosh (1766-1843), inventor of a waterproofing process (patent #4804, June 17, 1823). The surname is from Gaelic Mac an toisich "Son of the chieftain."
waterproof outercoat or raincoat, named after a Scottish chemist, Charles Macintosh (1766-1843), who invented the waterproof material that bears his name. The fabric used for a mackintosh was made waterproof by cementing two thicknesses of it together with rubber dissolved in a coal-tar naphtha solution