Search Result for "dark horse":
Wordnet 3.0

NOUN (2)

1. a political candidate who is not well known but could win unexpectedly;

2. a racehorse about which little is known; 



WordNet (r) 3.0 (2006):

dark horse
    n 1: a political candidate who is not well known but could win
         unexpectedly
    2: a racehorse about which little is known