adjective

1. 1. extremely poisonous or injurious; deadly
   2. bitterly antagonistic or spiteful; full of hate and enmity; venomous; rancorous
2. Med.
   1. violent and rapid in its course; highly malignant: said of a disease
   2. able to overcome the natural defenses of the host; highly infectious: said of a microorganism

Etymology: ME < L virulentus, full of poison < virus: see virus