The word "tord" does not appear to be a recognized English word. It might be a typographical error or a misinterpretation of another term. Based on the context you provided, it seems like you are looking for the meaning of a different term related to the given sentence about runners struggling to reach a finish line.
From the options you've listed, "relentless" seems to fit best with the idea of runners being challenged by difficult conditions. "Frightening" could also apply in a different context, but "relentless" suggests a constant and unyielding challenge, which aligns more closely with the runners' struggle.
If you meant a different word or if "tord" is used in a specific context or specialized jargon, please provide additional details!