an informant who exposes wrongdoing within an organization in the hope of stopping it; "the law gives little protection to whistleblowers who feel the public has a right to know what is going on"; "the whistleblower was fired for exposing the conditions in mental hospitals"
(bridge) a playing card with a value sufficiently high to insure taking a trick in a particular suit; "if my partner has a spade stopper I can bid no trump"
close or secure with or as if with a stopper; "She stoppered the wine bottle"; "The mothers stoppered their babies' mouths with pacifiers"