Etymology
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mettle (n.)

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.

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mettlesome (adj.)

"full of spirit, fiery, courageous," 1660s, from mettle + -some (1). Related: Mettlesomely; mettlesomeness.

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essay (v.)

"to put to proof, test the mettle of," late 15c., from French essaier, from essai "trial, attempt" (see essay (n.)). This sense has mostly gone with the divergent spelling assay. Meaning "to attempt" is from 1640s. Related: Essayed; essaying.

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brio (n.)

"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.

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spunk (n.)
1530s, "a spark," Scottish, from Gaelic spong "tinder, pith, sponge," from Latin spongia (see sponge (n.)). The sense of "courage, pluck, mettle" is first attested 1773. A similar sense evolution took place in cognate Irish sponnc "sponge, tinder, spark; courage, spunk." Vulgar slang sense of "seminal fluid" is recorded from c. 1888.
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prance (v.)

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.

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-some (1)

word-forming element used in making adjectives from nouns or adjectives (and sometimes verbs) and meaning "tending to; causing; to a considerable degree," from Old English -sum, identical with some, from PIE root *sem- (1) "one; as one, together with." Cognate with Old Frisian -sum, German -sam, Old Norse -samr; also related to same. "It usually indicates the possession of a considerable degree of the quality named: as mettlesome, full of mettle or spirit; gladsome, very glad or joyous" [Century Dictionary]. For the -some used with numbers (twosome, foursome, etc.), see -some (2).

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