1. One who achieves unexpected support and success as a political candidate, typically during a party's convention.
2. A little-known, unexpectedly successful entrant, as in a horserace.

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.