资料来源 : Webster's Revised Unabridged Dictionary (1913)

Mettlesome \Met"tle*some\, a.
   Full of spirit; possessing constitutional ardor; fiery; as, a
   mettlesome horse. -- {Met"tle*some*ly}, adv. --
   {Met"tle*some*ness}, n.

资料来源 : WordNet®

mettlesomeness
     n : courageous high-spiritedness