The ability to meet a challenge or persevere under demanding circumstances; determination or resolve: a race that tested the best runners' mettle.
on (one's) mettle
Prepared to accept a challenge and do one's best.
[Variant of METAL.]
Word History: Not only do metal and mettle have exactly the same pronunciation, the two terms are—etymologically, at least—exactly the same word. Middle English borrowed metal from Old French in the 1200s; Old French metal, metail, came from Latin metallum, from Greek metallon, "mine, quarry, ore, metal." By the 1500s, English metal had also come to mean "the stuff one is made of, one's character," but there was no difference in spelling between the literal and figurative senses until about 1700, when the spelling mettle, originally just a variant of metal, was fixed for the sense "strength of character." English has numerous examples of similar word pairs that are (historically speaking) spelling variants of the same word, including flour/flower and lightening/lightning.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.