UNYIELDING
unyielding
(adjective) resistant to physical force or pressure; “an unyielding head support”
dogged, dour, persistent, pertinacious, tenacious, unyielding
(adjective) stubbornly unyielding; “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”
Source: WordNet® 3.1
Etymology
Adjective
unyielding (comparative more unyielding, superlative most unyielding)
Not giving in; not bending; stubborn.
Synonym: Thesaurus:obstinate
Source: Wiktionary