· unwilling or unable to forgive or show mercy; "a surly unforgiving old woman"
Antonym(s): forgiving
· not to be placated or appeased or moved by entreaty; "grim determination"; "grim necessity"; "Russia's final hour, it seemed, approached with inexorable certainty"; "relentless persecution"; "the stern demands of parenthood"
Synonym(s): grim, inexorable, relentless, stern, unappeasable, unrelenting