My understanding is that both words refer to a hard-charging "take no prisoners" approach to an issue.Relentless is defined as, "showing or promising no abatement of severity, activity, strength or pace," and ruthless as "having no pity."
My further understanding is that "relentless" is more "honorable" than "ruthless." Examples:
In a "relentless" pursuit of her career, she stabbed people in the belly.
In a "ruthless" pursuit of his career, he stabbed people in the back.
Is this the correct distinction? Are the words more similar than this? Or do I have the wrong connotation for one or both words?
Edit1: A commenter defined ruthless as "having no pity", and relentless was "showing or promising no abatement of severity, intensity, strength, or pace" or "oppressively constant; incessant" (respectively) using dictionary definitions. which corresponds with my own research. IMHO, the two definitions are synonymous. If that's not the case, I am genuinely confused. My understanding of the difference between the two is the "honorable" part cited in the previous paragraph. Is this, indeed, the case?
Edit2: In answer to the commenter's later comment, I believe that a person who is single-mindedly "relentless" also "shows no pity" (his definition of ruthless). That may be wrong of course, but that's part of the basis of my question.
Edit3: This source considers the two words synonyms.
Best Answer
“Relentless” has a connotation of persistence and not able to be easily stopped by physical challenges.
“Ruthless” has the connotation of not being stopped by moral or ethical considerations.
A hero who chases a villain no matter what is relentless; if s/he is willing to injure or kill innocent people to capture the villain, he or she is ruthless.