WordNet sense 1 (extremely poisonous or injurious; producing venom):

deadly, virulent

WordNet sense 2 (of or relating to or caused by a toxin or poison):

toxic

WordNet sense 3 (harsh or corrosive in tone):

acerbic, acid, acrid, bitter, blistering, caustic, sulfurous, vitriolic, acerb, sulphurous

WordNet sense 4 (disagreeable to the senses, to the mind, or feelings ):

unpleasant

WordNet sense 5 (marked by deep ill will; deliberately harmful):

poisonous, vicious

WordNet sense 6 (having the nature of or resulting from malice):

malicious