UNFORGIVING
unforgiving
(adjective) unwilling or unable to forgive or show mercy; “a surly unforgiving old woman”
grim, inexorable, relentless, stern, unappeasable, unforgiving, unrelenting
(adjective) 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”
Source: WordNet® 3.1
Etymology
Adjective
unforgiving (comparative more unforgiving, superlative most unforgiving)
Unwilling or unable to forgive or show mercy.
Having no allowance for weakness.
Source: Wiktionary