The Oxford Thesaurus An A-Z Dictionary of Synonyms - remorselessadj.

1) cruel, heartless, callous, harsh, hard-hearted, stony-hearted, savage, merciless, unmerciful, pitiless, ruthless: The heavyweight champion administered a remorseless beating to the challenger. 2) relentless, unrelenting, unremitting, unstoppable, inexorable, implacable: The remorseless storm thrashed at our tiny vessel, tearing away every last shred of rigging.