Source : Webster's Revised Unabridged Dictionary (1913)

Heinous \Hei"nous\, 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 great offense; -- applied to deeds or to character.

         It were most heinous and accursed sacrilege. --Hooker.

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

   Syn: Monstrous; flagrant; flagitious; atrocious. --
        {Hei"nous*ly}, adv. -- {Hei"nous*ness}, n.

Source : WordNet®

heinous
     adj : shockingly brutal or cruel; "murder is an atrocious crime";
           "a grievous offense against morality"; "a grievous
           crime"; "no excess was too monstrous for them to
           commit" [syn: {atrocious}, {flagitious}, {grievous}, {monstrous}]