Definition of mithril in English:

mithril

Pronunciation /ˈmɪθrɪl/

noun

  • In the fiction of J. R. R. Tolkien (subsequently adopted in other fantasy contexts with reference to Tolkien): a rare silver-coloured precious metal of great hardness and beauty.

    The word was coined during the composition of The Lord of the Rings (1940: see C. Tolkien Treason of Isengard (1989) ix. 184). It did not appear in the first or second edition of The Hobbit.

Origin

1940s; earliest use found in J. R. R. Tolkien (1892–1973), writer and philologist. An arbitrary formation, explained by J. R. R. Tolkien in relation to other words in his invented Elvish language.