Source : Webster's Revised Unabridged Dictionary (1913)

Noxious \Nox"ious\, a. [L. noxius, fr. noxa harm; akin to nocere
   to harm, hurt. Cf. {Nuisance}, {Necromancy}.]
   1. Hurtful; harmful; baneful; pernicious; injurious;
      destructive; unwholesome; insalubrious; as, noxious air,
      food, or climate; pernicious; corrupting to morals; as,
      noxious practices or examples.

            Too frequent an appearance in places of public
            resort is noxious to spiritual promotions. --Swift.

   2. Guilty; criminal. [R.]

            Those who are noxious in the eye of the law. --Abp.
                                                  Bramhall.

   Syn: Noisome; hurtful; harmful; injurious; destructive;
        pernicious; mischievous; corrupting; baneful;
        unwholesome; insalubrious. See {Noisome}. --
        {Nox"ious*ly}, adv. -- {Nox"ious*ness}, n.

Source : WordNet®

noxious
     adj : injurious to physical or mental health; "noxious chemical
           wastes"; "noxious ideas" [syn: {harmful}] [ant: {innocuous}]