from The American Heritage® Dictionary of the English Language, 4th Edition
- n. One who achieves unexpected support and success as a political candidate, typically during a party's convention.
- n. A little-known, unexpectedly successful entrant, as in a horserace.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A candidate who is nominated unexpectedly, without previously having been discussed or considered as a likely choice.
- n. An unexpected success.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a political candidate who is not well known but could win unexpectedly
- n. a racehorse about which little is known
Originally an allusion to an unknown horse winning a race, as used in an 1831 novel The Young Duke by Benjamin Disraeli. (Wiktionary)