Virulent
VIR'ULENT, adjective [Latin virulentus, from virus, poison, that is, strength, from the same root as vir, vireo. See Venom.]
1. Extremely active in doing injury; very poisonous or venomous. No poison is more virulent than that of some species of serpents.
2. Very bitter in enmity; malignant; as a virulent invective.