[adj] having austere inflexibility; "a flinty manner"; "granitic morality"; "his unyielding mouth and glassy eyes"- Marchette Chute
[adj] refusing to give way or compromise; "unyielding determination"
[adj] stubbornly unyielding; "dogged persistence"; "dour determination"; "the most vocal and pertinacious of all the critics"; "a mind not gifted to discover truth but tenacious to hold it"- T.S.Eliot; "men tenacious of opinion"