If you describe someone as merciless, you mean that they are very cruel or determined and do not show any concern for the effect their actions have on other people. the merciless efficiency of a modern police state. = ruthless + mercilessly mer·ci·less·ly We teased him mercilessly
having or showing no mercy; "the merciless enemy"; "a merciless critic"; "gave him a merciless beating"
having or showing no mercy; "the merciless enemy"; "a merciless critic"; "gave him a merciless beating