a.
1.
Inflexible, constant, steady, resolute, steadfast, stanch, pertinacious, determined, indomitable.
2.
Stubborn, stiff, obstinate, wilful, headstrong, intractable, perverse, wayward.
3.
Stiff, rigid, stubborn, hard, firm, unbending.
UNYIELDING
Meaning of UNYIELDING in English
Soule. Dictionary of English synonyms. Словарь английских синонимов. 2012