Answer: malignant

AnswerCrossword Clue
MALIGNANTBent on evil.
malignantMalevolent
malignant(of a tumor) Tending to invade normal tissue or to recur after removal; cancerous
malignant(of a disease) Very virulent or infectious
malignantevil, malign / a supporter of the royalist cause during the English civil war