noun
mettle
MET-ul/ˈmetl/
Courage and strength of character in facing difficulties.
The volunteer shows his mettle by persisting with the heavy branch in the rain.

Etymology
Material or “stuff” became a metaphor for what a person is made of—the person's physical or moral constitution. That figurative meaning narrowed to spirit and courage, giving mettle its sense of determination under pressure.
In context
If we meet a powerful dark creature, it'll be a fine chance to test my mettle now.
More examples
- He proved his mettle by staying calm under pressure.
- The difficult assignment revealed the team’s mettle.
- She admired his mettle more than his easy successes.
Forms
mettle