"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"
2. refusing to give way or compromise;
"unyielding determination"
3. having austere inflexibility;
"a flinty manner""granitic morality""his unyielding mouth and glassy eyes"- Marchette Chute