adamant

/ˈa-də-mənt/

from attributive use of

adjective

  1. unshakable or insistent especially in maintaining a position or opinion : unyielding

an adamant insistence on doing things his own way

inflexible obdurate adamant mean unwilling to alter a predetermined course or purpose. inflexible implies rigid adherence or even servile conformity to principle. obdurate stresses hardness of heart and insensitivity to appeals for mercy or the influence of divine grace.

noun

  1. a stone (such as a diamond) formerly believed to be of impenetrable hardness

  2. an unbreakable or extremely hard substance