1. 
2. 
[syn: grim, inexorable, relentless, stern, unappeasable, unforgiving, unrelenting]
The Collaborative International Dictionary of English v.0.48:
Unforgiving \Unforgiving\
   See forgiving.
WordNet (r) 3.0 (2006):
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,
       unforgiving, unrelenting]
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