substance or quality of temperament; spirit, especially. 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.
Origin: E. Metal, used in a tropical sense in allusion to the temper of the metal of a sword blade. See Metal.