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

venomous

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 ((of a disease) having a rapid course and violent effect):

deadly