Adamantine

Word of the Day for Friday, February 24, 2012

adamantine \ad-uh-MAN-teen\, adjective:

1. Utterly unyielding or firm in attitude or opinion.
2. Too hard to cut, break, or pierce.
3. Like a diamond in lustre.

That will shock some people at the Folger, but Shakespeare is adamantine.
-- Tad Friend, "Compleat Works," The New Yorker, Jan. 9, 2012

…and when she saw the state his clothes were in her resolution to turn his Saturday holiday into captivity at hard labour became adamantine in its firmness.
-- Mark Twain, The Adventures of Tom Sawyer

Related to adamant, adamantine comes from the Greek word adamántinos, a combination of the word adamant and the suffix -ine which means "of or pertaining to."

Thanks to: http://www.dictionary.com/