Webster's Revised Unabridged Dictionary · 1913

Mettle

Mettle , noun

[English metal, used in a tropical sense in allusion to the temper of the metal of a sword blade. See Metal.]

Substance or quality of temperament; spirit, esp. as regards honor, courage, fortitude, ardor, etc.; disposition; -- usually in a good sense; as, to test a person's mettle.
A certain critical hour which shall... try what mettle his heart is made of. — South
Gentlemen of brave mettle. — Shakespeare
The winged courser, like a generous horse, Shows most true mettle when you check his course. — Pope
Collocations (1)
To put one one's mettle , to cause or incite one to use one's best efforts.