say it: KOH-stur
coaster is a noun meaning "a resident of a coastal area". It carries 3 recorded senses.
a resident of a coastal area
someone who coasts
a covering (plate or mat) that protects the surface of a table (i.e., from the condensation on a cold glass or bottle)
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for coaster come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.