1580s, a variant spelling of metal. Both forms of the word were used interchangeably (by Shakespeare and others) in the literal sense and in the figurative one of "stuff of which a person is made, (a person's) physical or moral constitution" (1550s), hence "natural temperament," specifically "ardent masculine temperament, spirit, courage" (1590s). The spellings diverged early 18c. and this form took the figurative sense. Related: Mettled.
"liveliness, vivacity," 1734, from Italian brio "mettle, fire, life," perhaps a shortened derivative of Latin ebrius "drunk." Or via Provençal briu "vigor," from Celtic *brig-o- "strength," from PIE root *gwere- (1) "heavy." Probably it entered English via the musical instruction con brio.
late 14c., prauncen, originally of horses in high mettle, "make a show in walking; move proudly, lifting the feet with a capering motion," a word of unknown origin. By late 14c. of persons, "to strut, swagger, act proudly and aggressively."
Perhaps related to Middle English pranken "to show off" (from Middle Dutch pronken "to strut, parade;" see prank) by influence of dance (though prank is not attested as early as this word); or perhaps from Danish dialectal prandse "to go in a stately manner." Klein suggests Old French paravancier. Related: Pranced; prancing. As a noun from 1751, from the verb.