01 n. Substance or quality of temperament; spirit, esp. as regards honor, courage, fortitude, ardor, etc.; disposition; -- usually in a good sens…
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1.
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.” — Shak.“The winged courser, like a generous horse, Shows most true mettle when you check his course.” — Pope.
Phrases & compounds
To put one one's mettle —
to cause or incite one to use one's best efforts.