a.
1.
Stiff, rigid.
2.
Pertinacious, dogged, stubborn, obstinate, unyielding, refractory, headstrong, wilful, cantankerous, intractable, heady, obdurate, cross-grained.
3.
Firm, resolute, steadfast, immovable, persevering.
4.
Inexorable, unyielding, immovable by entreaties.