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

obnoxious \obnox"ious\ o^bno^k"shu^s, a. l. obnoxius;
   ob see ob- + noxius hurtful. see noxious.
   1. subject; liable; exposed; answerable; amenable; -- with
      to.
      1913 webster

            the writings of lawyers, which are tied obnoxious to
            their particular laws.                --bacon.
      1913 webster

            esteeming it more honorable to live on the public
            than to be obnoxious to any private purse. --milton.
      1913 webster

            obnoxious, first or last,
            to basest things                      --milton.
      1913 webster

   2. liable to censure; exposed to punishment; reprehensible;
      blameworthy. "the contrived and interested schemes of . .
      . obnoxious authors." --bp. fell.
      1913 webster

            all are obnoxious, and this faulty land,
            like fainting hester, does before you stand
            watching your scepter.                --waller.
      1913 webster

   3. very offensive; odious; hateful; as, an obnoxious
      statesman; a minister obnoxious to the whigs. --burke.
      1913 webster -- obnox"iously, adv. --
      obnox"iousness, n. --south.
      1913 webster
see also:
ob- noxious obnox"iously obnox"iousness 

[2] : WordNet (r) 2.0

obnoxious
     adj : causing disapproval or protest; "a vulgar and objectionable
           person" syn: objectionable, unpleasant
see also:
objectionable unpleasant 

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

123 moby thesaurus words for "obnoxious":
   abhorrent, abject, abominable, arrant, atrocious, awful, base,
   beastly, beggarly, below contempt, beneath contempt, blameworthy,
   brutal, cheesy, contemptible, crude, crummy, debased, degraded,
   deplorable, depraved, despicable, detestable, dire, dirty,
   disgusting, dreadful, egregious, enormous, execrable, exposed,
   fetid, filthy, flagrant, forbidding, foul, fulsome, grave,
   grievous, gross, hateful, heinous, horrible, horrid, ignoble,
   infamous, invidious, lamentable, little, loathsome, lousy, low,
   low-down, lumpen, malodorous, mangy, mean, measly, mephitic,
   miasmal, miasmic, miserable, monstrous, nasty, nauseating,
   nefarious, noisome, notorious, noxious, objectionable, obscene,
   odious, offensive, open, outrageous, paltry, petty, pitiable,
   pitiful, poky, poor, prone, rank, rebarbative, regrettable,
   repellent, reprehensible, reptilian, repugnant, repulsive,
   revolting, revulsive, rotten, sad, scabby, scandalous, schlock,
   scrubby, scruffy, scummy, scurvy, sensitive, shabby, shameful,
   shocking, shoddy, sickening, small, sordid, squalid, stinking,
   subject, susceptible, terrible, too bad, unclean, unmentionable,
   vile, villainous, woeful, worst, worthless, wretched

Obnoxious >> O Words
Obnoxious, definition of term: Obnoxious
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