\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.