yìng​gǔ​tou

resolute person

硬骨头 (硬骨頭) yìng​gǔ​tou
resolute person noun
a person of unyielding character or integrity who does not succumb to pressure
tough task noun
a difficult problem to solve or a hard nut to crack

Frequency

Movie subtitles
0.420 per million appears in 0% of films
Written text
0.980 per million

Sources

Definitions
CC-CEDICT