from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. One who reports a problem or violation to the authorities; especially, an employee or former employee who reports a violation by an employer.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. an informant who exposes wrongdoing within an organization in the hope of stopping it
Probably an allusion to a police officer blowing his or her whistle on observing a violation of the law. (Wiktionary)