From Longman Dictionary of Contemporary Englishboaterboat‧er /ˈbəʊtə $ ˈboʊtər/ noun [countable] 
DCa hard straw hat with a flat top
DCa hard straw hat with a flat topExamples from the Corpus
boater• They are a magnet for tourists, experienced boaters and amateurs alike.• Enough fuel leaked into the lake that nearby boaters could see the shiny residue and smell the gasoline.• Removal of the straw boater revealed a head of sleeked-down dark hair - a man's head of hair.• The boat was towed to Sausalito and the boater was uninjured.• Marine manufacturers are really listening to what boaters want, and the hot new trends prove it.• State regulations require whitewater boaters to wear helmets and life vests.• The men wore boaters and blazers, the women summer dresses.Origin boater (1800-1900) Because it was originally used for boating 