mettle

Etymology

From figurative use of metal (since 16th century). The two spellings were originally interchangeable variants, but came to be distinguished by sense in the 18th century.

noun

1. A quality of endurance and courage.
   Please read on and discover the issues in education that test the mettle of those who experience this world every day. 2001, Harry J. Alexandrowicz, Testing your Mettle: Tough Problems and Real-world Solutions for Middle and High School Teachers, page xiii
   Its possible that some traders will become less interested as their offline lives resume more fully, but their mettle may really be tested when the market runs into its next downturn. 2021-04-28, Tara Siegel Bernard, “Trading Stock Tips on TikTok, Newbies Are Deeply Invested in Learning”, in The New York Times, →ISSN
2. Good temperament and character.
3. Obsolete spelling of metal (“metallic substance”)

adj

1. (Scotland) Spirited, vigorous, stout-hearted.
   And then one afternoon in the hinder end of April came young Heriotside riding to the Skerburnfoot. His arm was healed, he had got him a fine new suit of green, and his horse was a mettle beast that well set off his figure. 1902, John Buchan, The Outgoing of the Tide