dark horse

English Thesaurus

1. a racehorse about which little is known (noun.animal)

hypernym	:	bangtail, race horse, racehorse,
definition	:	a horse bred for racing (noun.animal)

2. a political candidate who is not well known but could win unexpectedly (noun.person)

hypernym	:	campaigner, candidate, nominee,
definition	:	a politician who is running for public office (noun.person)