WordNet sense 1 (incapable of adapting or changing to meet circumstances):

unbending

WordNet sense 2 (not adaptable):

unadaptable

WordNet sense 3 (not making concessions):

sturdy, uncompromising

WordNet sense 4 (impervious to pleas, persuasion, requests, reason):

adamant, inexorable

WordNet sense 5 (incapable of or resistant to bending):

rigid, stiff