The Collaborative International Dictionary of English v.0.48:

Heinous \Hei"nous\ (h[=a]"n[u^]s), a. [OF. ha["i]nos hateful, F.
   haineux, fr. OF. ha["i]ne hate, F. haine, fr. ha["i]r to
   hate; of German origin. See Hate.]
   Hateful; hatefully bad; flagrant; odious; atrocious; giving
   great offense; -- applied to deeds or to character.
   [1913 Webster]

         It were most heinous and accursed sacrilege. --Hooker.
   [1913 Webster]

         How heinous had the fact been, how deserving
         Contempt!                                --Milton.

   Syn: Monstrous; flagrant; flagitious; atrocious. --
        Hei"nous*ly, adv. -- Hei"nous*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

heinous
    adj 1: extremely wicked, deeply criminal; "a flagitious crime";
           "heinous accusations" [syn: flagitious, heinous]

Moby Thesaurus II by Grady Ward, 1.0:

140 Moby Thesaurus words for "heinous":
   abhorrent, abject, abominable, arrant, atrocious, awful, bad, base,
   beastly, beggarly, below contempt, beneath contempt, black,
   blamable, blameworthy, brutal, cheesy, contemptible, criminal,
   crude, crummy, crying, damnable, dark, debased, degraded,
   deplorable, depraved, desperate, despicable, detestable, dire,
   dirty, disgraceful, disgusting, dreadful, egregious, enormous,
   evil, execrable, fetid, filthy, flagitious, flagrant, forbidding,
   foul, fulsome, grave, grievous, gross, hateful, horrible, horrid,
   ignoble, improper, infamous, iniquitous, knavish, lamentable,
   little, loathsome, lousy, low, low-down, lumpen, malodorous, mangy,
   mean, measly, mephitic, miasmal, miasmic, miserable, monstrous,
   nasty, naughty, nauseating, nefarious, noisome, notorious, noxious,
   objectionable, obnoxious, obscene, odious, offensive, outrageous,
   paltry, peccant, petty, pitiable, pitiful, poky, poor, rank,
   rebarbative, regrettable, repellent, reprehensible, reprobate,
   reptilian, repugnant, repulsive, revolting, rotten, sad, scabby,
   scandalous, schlock, scrubby, scruffy, scummy, scurvy, shabby,
   shameful, shocking, shoddy, sickening, sinful, small, sordid,
   squalid, stinking, terrible, too bad, unclean, unforgivable,
   unmentionable, unpardonable, unspeakable, unworthy, vicious, vile,
   villainous, wicked, woeful, worst, worthless, wretched, wrong