unmerciful
1. [ adjective ] having or showing no mercy
Synonyms: merciless
Examples:

"the merciless enemy" "a merciless critic" "gave him a merciless beating"

Related terms: merciful pitiless cutthroat tigerish mortal hard bloody implacable unkind uncompassionate inclement
Similar spelling:   unmercifully
  unregretful
  unresentful
  unreactive