Which word describes someone who is unwilling to give up easily on a certain principle?

The word that best describes someone who is unwilling to give up easily on a certain principle is tenacious. This term implies a strong determination and a persistent attitude, especially in the face of difficulties or obstacles. A tenacious individual holds on firmly to their beliefs and values, demonstrating grit and resilience in their endeavors.

While resolute and steadfast share similar connotations of determination, tenacious specifically emphasizes the unyielding grip one has on their principles. Resolute suggests a determined mindset but doesn't always capture the idea of perseverance against challenges as strongly as tenacious does. Steadfast conveys loyalty and unwavering support but may not necessarily imply a struggle against adversity, which is intrinsic to being tenacious. Faithful primarily relates to loyalty and devotion without the emphasis on determination against challenges or principles.