From Longman Dictionary of Contemporary Englishcoastercoast‧er /ˈkəʊstə $ ˈkoʊstər/ noun [countable] 1 DFDa small thin object on which you put a glass, or cup, to protect a table from heat or liquids2 TTWa ship that sails from port to port along a coast, but does not go further out to sea → roller coaster
Examples from the Corpus
coaster• Beside him, the old cook Chucha is fussing with a coaster for his glass.• Cons: Only one coaster so loading is slow.• I know people who like to lean over the edge of observation towers or ride the tallest roller coasters without holding on.• He turned the glass slowly on the coaster as he thought about her.From Longman Business Dictionarycoastercoast‧er /ˈkəʊstəˈkoʊstər/ (also coasting ship British English, coasting vessel British English) noun [countable]TRANSPORT a small ship that carries goods between ports within a country, but does not go to foreign portsA small coaster was discharging timber. 