dark horse
US /dɑrk hɔrs/
UK /dɑrk hɔrs/

1.
kuda hitam, orang yang tidak dijangka
a person who keeps their abilities and intentions secret and who surprises people by doing something unexpected, especially by winning a competition or election
:
•
No one expected him to win; he was a real dark horse in the race.
Tiada siapa menjangka dia akan menang; dia adalah kuda hitam sebenar dalam perlumbaan itu.
•
She's a bit of a dark horse; you never know what she's going to do next.
Dia agak misteri; anda tidak pernah tahu apa yang akan dia lakukan seterusnya.