relentless

a.无情的，不仁慈的，残酷的

relate, relate...to, related, relatedness, relation, relationship, relative, relatively, relativism, relativistic, relativity, relax, relaxation, relaxed, relaxing, relay, release, relegate, relegation, relent, relentlessly, relentlessness, relevance, relevant, reliability, reliable, reliably, reliance, reliant, relic, relief, relief map, relief road, relieve, relieve sb. of, relieved, religion, religious, religiously, religiousness,