If you refer to someone or something as noxious, you mean that they are extremely unpleasant. the heavy, noxious smell of burning sugar, butter, fats, and flour Their behaviour was noxious. harmful or poisonous = toxic (noxius, from noxa )
harmful (usually to agriculture); plants, animals and insects may be declared noxious by legislation, and farmers and organisations are expected to attempt to eradicate or control the noxious species