dark

a dark horse a person, especially a competitor, about whom little is known.

☞ The expression was originally horse-racing slang. The earliest recorded use was by Benjamin Disraeli in 1831: 'A dark horse, which had never been thought of…rushed past the grand stand in sweeping triumph'.

keep someone in the dark ensure that someone remains in a state of ignorance about something.

2003Village Voice It's payback time for an administration that…has ignored lawmakers and…deliberately kept them in the dark.

keep something dark keep something secret from other people.

1993New York Review of Books Ottoline was determined to keep her affair with Russell safe from Bloomsbury's prying eyes and she and Russell went to Feydeauesque lengths to keep their secret dark.

a leap in the dark: seeleap.

a shot (or stab) in the dark an act whose outcome cannot be foreseen; a mere guess.

☞ The metaphorical use of in the dark to mean 'in a state of ignorance' dates from the late 17th century.

whistle in the dark: seewhistle.