Deadly
Part of speech: adjective
Definition: lethal very accurate (of aiming with a bow, firearm, etc.) very boring excellent, awesome, cool
Part of speech: adverb
Definition: Fatally, mortally. In a way which suggests death.
Example sentence: The Cold War isn't thawing; it is burning with a deadly heat. Communism isn't sleeping; it is, as always, plotting, scheming, working, fighting.
Virulent
Part of speech: adjective
Definition: Of a disease or disease-causing agent, highly infectious, malignant, or deadly.Hostile to the point of being venomous; intensely acrimonious.