Differences between "sleeper" and "dark horse"

Question

I was wondering what the differences are between sleeper and dark horse.

Are they interchangeable while having similar meanings?

Are there other similar words?

Answer 1

From New Oxford American:

dark horse |ˈdɑrk ˈˈhɔrs|
noun
1 a person about whom little is known, esp. someone whose abilities and potential for success are concealed : [as adj.] a dark-horse candidate.
2 a competitor or candidate who has little chance of winning, or who wins against expectations : a preseason dark horse as the nation's top collegiate football team.

sleeper |ˈslipər|
noun
3 a movie, book, play, etc., that achieves sudden unexpected success after initially attracting little attention, typically one that proves popular without much promotion or expenditure.
• an antique whose true value goes unrecognized for some time.

From Etymonline:

dark horse
in politics, 1842, an image from horse racing, in which dark is used in its figurative sense of "unknown."

Moonraker is called a "dark horse"; that is neither his sire nor dam is known. ["Pierce Egan's Book of Sports," London, 1832]

sleeper
[...] Sense of "something whose importance proves to be greater than expected" first attested 1892, originally in Amer.Eng,. sports jargon, probably from earlier gambling slang (1856) sense of "unexpected winning card."

Here's some generalizations gleaned from the above:

• dark horses are usually people; sleepers are usually things.
• dark horses are intentionally kept unknown; sleepers are simply not promoted.
• a dark horse might achieve success; a sleeper already has—surprisingly.
• dark horses' limelight often decrescendoes; sleepers' crescendoes.

As to your questions, I'd say they're not quite interchangeable. Knowing their different connotations will likely prove one to be the better word choice.

A dark horse might also be called an enigma, or simply an unknown; while surprise hit, cult classic, and box-office success are other phrases often applied to sleepers.

Answer 2

There are very slight differences. Usually they are interchangeable, however, "dark horse" has a nuance that "sleeper does not have.
"Dark horse" has the connotation that whoever is being called "dark horse", is unexpected to win, but wins, where as "sleeper" has the connotation that person is unknown, but wins unexpectedly.

In other words, a "dark horse" is someone who is expected to "not win", but a "sleeper" is just a person who wins unexpectedly, but no one has previously expected it to "not win".

As in:
"John was expected to be one of the losers. He expected not to win. However, John came out first. John is a dark horse."

"John wasn't well-known prior to this race. No one knew much about John, so they weren't sure John would win or not. It turns out that John did win. John is a sleeper."