Synonyms for Noxious:

adj.

dangerous (adjective)
pestilent.
deadly, injurious (adjective)
pestilent, harmful, unhealthy, putrid, poisonous, baneful, venomous, corrupting, unwholesome, insalubrious, pernicious, virulent, toxic.
evil (adjective)
corrupting.
harmful (adjective)
risky, poisonous.
unhealthy (adjective)
gangrenous, unwholesome, pathological, diseased, contagious, septic, insalubrious, unhealthy, infected, deadly, unsanitary, toxic, unhygienic, poisonous, malignant, pestilent, contaminated.

n.

hazardous, disastrous, risky, unsafe, perilous. help, virulent. foul (noun)
rotten, offensive, putrid.
noxious (noun)
degrading, pestilent, vesicatory, corrupting, deadly, vesicant, pernicious, baneful, harmful.
poisonous (noun)
venomous, virulent.

v.

revolting (verb)
offensive.

Other synonyms:

virulent. Other relevant words:
offensive, degrading, venomous, putrid, pernicious, baneful, vesicatory, corrupting, vesicant, disastrous, harmful, virulent, rotten.

Usage examples for noxious

  1. It was perhaps that which made me faint; but as I did not feel any other ill effects, I began to hope that, either in passing through my jacket the poison had been scraped off, or that it has, as I have heard, but slight noxious effects on salt- eating Europeans." – On the Banks of the Amazon by W.H.G. Kingston
  2. Carefully he opened the top and gazed down, starting back a second later, with his face puckered up at the noxious odor. – The Exploits of Elaine by Arthur B. Reeve
  3. Diomed, one of the richest men of Pompeii, abandoned his wife and daughters and was fleeing with a bag of silver when he was stifled in front of his garden by noxious vapors. – Round-about Rambles in Lands of Fact and Fancy by Frank Richard Stockton