from Wiktionary, Creative Commons Attribution/Share-Alike License
- v. To disclose information to the public or to appropriate authorities concerning the illegal or socially harmful actions of a person or group, especially a corporation or government agency.
- v. To make a piercing sound which signals a referee's action or the end of a game.
When used idiomatically, probably an allusion to a police officer blowing his or her whistle on observing a violation of the law. (Wiktionary)