dark horse

plural dark horses

1. idiomaticSomeone who possesses talents or favorable characteristics that are not known or expected by others.

   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 more examples

   ‘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

   “Well!” Genevieve laughs – the kind of bright, trilling laugh you give when you’re really quite annoyed about something. “Ed, you are a dark horse! I had no idea you had a girlfriend!”

   2009, Sophie Kinsella, Twenties Girl: A Novel, London: Black Swan, published 2010, →ISBN, page 183

2. idiomaticgovernmentA 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. hobbiesA horse whose capabilities are not known.
4. Used other than figuratively or idiomatically: see dark, horse.