▸ noun: a covering (plate or mat) that protects the surface of a table (i.e., from the condensation on a cold glass or bottle)
▸ noun: someone who coasts
▸ noun: a resident of a coastal area
▸ name: A surname (very rare: popularity rank in the U.S.: #44239)
http://www.onelook.com/?w=coaster&ls=acoaster (plural coasters)
Something that coasts, such as a sled or toboggan.
(nautical) A merchant vessel that stays in coastal waters.
A small piece of material used to protect the surface of a table, upon which one places cups or mugs.
A small tray on wheels, used to pass something around a table.
(computing, slang) A worthless compact disc, such as one that was burned incorrectly.
https://en.wiktionary.org/wiki/coaster