Synonyms and related words :
dour, firm, fundamentalist, hard, hidebound, impliable, inexorable, inflexible, iron, ironbound, ironclad, ironhanded, muscle-bound, obdurate, obstinate, orthodox, procrustean, purist, puristic, puritan, puritanic, relentless, rigid, rigorist, rigoristic, rigorous, rockbound, stiff, straitlaced, stubborn, unbending, uncompromising, unrelenting, unyielding