dark horse

Noun

dark horse (plural dark horses)

1. (idiomatic) Someone who possesses talents or favorable characteristics that are not known or expected by others.
   • ‘She’s a dark horse,’ he said. ‘She knows just as much about climbing mountains as you or I. In fact, she was ahead of me the whole time, and I lost her.’1952, Daphne Du Maurier, “Monte Verità”, in The Apple Tree
   • As she pulled the door closed behind her, she heard the nurse say, “Well! You’re a dark horse, I must say! Do you know that extraordinary-looking girl?”2005, Steve Augarde, Celandine, London: Corgi Books, published 2006, →ISBN, page 13
2. (idiomatic) A candidate for an election who is nominated unexpectedly, without previously having been discussed or considered as a likely choice.
   • That left Cardinal Robert Francis Prevost, 69 — a quiet American dark horse who had, surprisingly, emerged in the evening’s vote — as a source of particular interest.2025 May 11, Jason Horowitz, Emma Bubola, Elizabeth Dias, Patricia Mazzei, “How a Quiet American Cardinal Became Pope”, in The New York Times, →ISSN
3. A horse whose capabilities are not known.
4. Used other than figuratively or idiomatically: see dark, horse.