Noah Webster
Mettle
METTLE, noun met'l. [usually supposed to be corrupted from metal.
Latin animus, animosus.] Spirit; constitutional ardor; that temperament which is susceptible of high excitement. It is not synonymous with courage, though it may be accompanied with it, and is sometimes used for it.
The winged courser, like a generous horse,
Shows most true mettle when you check his course.