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"
You describe someone as unyielding when they have very strong, fixed ideas about something and are unlikely to change their mind. The authorities proved unyielding on one crucial opposition demand His unyielding attitude on this subject was that since he had done it, so could everyone
If a barrier or surface is unyielding, it is very solid or hard. the troopers, who had to build roads through those unyielding mountains He sat on the edge of an unyielding armchair, a cup of tea in his hand