1. An infallible means of attack or defense.
2. A simple remedy for a difficult or intractable problem: "There is no single silver bullet or panacea that will solve all the problems of Bay Area schools" (San Francisco Chronicle).

[From the belief that werewolves could be killed with silver bullets.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.