unyielding
Not willing to bend, change, or give in.
Unyielding means refusing to bend, give way, or change, no matter how much pressure is applied. Picture trying to bend a thick steel rod with your bare hands: it won't budge. That rod is unyielding.
The word describes both physical things and people's attitudes. An unyielding material like concrete or granite won't flex or compress easily. An unyielding person sticks firmly to their position and won't compromise or back down. A judge might be unyielding in enforcing courtroom rules. A coach might have an unyielding commitment to practice schedules. Your grandmother might be unyielding in her insistence that you write thank-you notes.
Sometimes being unyielding shows strength and determination. A firefighter's unyielding courage in a dangerous situation saves lives. A scientist's unyielding pursuit of truth leads to important discoveries. Abraham Lincoln remained unyielding in his determination to preserve the Union during the Civil War.
But unyielding can also describe someone who is stubborn and unwilling to listen. Someone who won't consider other viewpoints might be described as unyielding, and that's not a compliment.