mettle
n. uncountablen. the quality of being brave and strong, especially when things get difficult. It is the ability to stay calm and do the right thing even when you are under pressure.
n. the quality of being brave, strong, and determined, especially in the face of adversity. Often used in the phrase 'to prove one's mettle' to describe demonstrating one's character or ability under pressure.
The firefighters showed great mettle during the storm.
The young team proved their mettle by winning the championship despite being the underdogs all season.
While the initial crisis was manageable, it was the subsequent weeks of uncertainty that truly tested the mettle of the leadership team.
From figurative use of metal (since 16th century). The two spellings were originally interchangeable variants, but came to be distinguished by sense in the 18th century.