[1] : The Collaborative International Dictionary of English v.0.48

unforgiving \unforgiving\
   see forgiving.
see also:
forgiving 

[2] : WordNet (r) 2.0

unforgiving
     adj 1: unwilling or unable to forgive or show mercy; "a surly
            unforgiving old woman" ant: forgiving
     2: 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" syn: grim,
         inexorable, relentless, stern, unappeasable, unrelenting
     3: harsh and severe; "i hope i'm not being uncharitable but he
        really is a bore"; "unjust and uncharitable criticism"
        syn: uncharitable
see also:
forgiving grim inexorable relentless stern unappeasable 
unrelenting uncharitable 

[3] : Moby Thesaurus II by Grady Ward, 1.0

25 moby thesaurus words for "unforgiving":
   bowelless, cruel, dog-eat-dog, flinty, hard, harsh, heartless,
   inclement, inexorable, merciless, pitiless, relentless,
   remorseless, ruthless, uncompassionate, uncompassioned, unfeeling,
   unmerciful, unpitiful, unpitying, unremorseful, unsympathetic,
   unsympathizing, unyielding, without mercy

Unforgiving >> U Words
Unforgiving, definition of term: Unforgiving
unforgiving_pag1.html