Met″tle (?), n. [E. 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.
A certain critical hour which shall... try what mettle his heart is made of. South.
Gentlemen of brave mettle. Shak.
The winged courser, like a generous horse,
Shows most true mettle when you check his course. Pope.
To put one one's mettle, to cause or incite one to use one's best efforts.