1. 
[syn: grim, inexorable, relentless, stern, unappeasable, unforgiving, unrelenting]
The Collaborative International Dictionary of English v.0.48:
Unappeasable \Unappeasable\
   See appeasable.
WordNet (r) 3.0 (2006):
unappeasable
    adj 1: 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:
62 Moby Thesaurus words for "unappeasable":
   a hog for, acquisitive, all-devouring, avaricious, avenging, avid,
   bottomless, coveting, covetous, devouring, esurient, gluttonous,
   gobbling, grabby, grasping, greedy, grudgeful, hoggish, implacable,
   insatiable, insatiate, irreconcilable, limitless, mercenary,
   merciless, miserly, money-hungry, money-mad, mortal, omnivorous,
   overgreedy, piggish, punitive, punitory, quenchless, rancorous,
   rapacious, ravening, ravenous, relentless, retaliatory, revanchist,
   revengeful, ruthless, slakeless, sordid, swinish, unappeased,
   unflinching, unquenchable, unrelenting, unsated, unsatisfiable,
   unsatisfied, unslakeable, unslaked, unyielding, venal, vengeful,
   vindicatory, vindictive, voracious