Something bad that is relentless never stops or never becomes less intense. 毫不留情的
adjective [原级] 坚韧的，不屈不挠的；残酷无情的，不留情面的；不停的，不间断的
Someone who is relentless is determined to do something and refuses to give up, even if what they are doing is unpleasant or cruel. 坚持不懈的
relent(变温和) + less → 不能变温和 → 无情的
