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c.1400, in reference to wounds, ulcers, etc., "full of corrupt or poisonous matter," from Latin virulentus "poisonous," from virus "poison" (see virus). Figurative sense of "violent, spiteful" is attested from c.1600. Related: Virulently.
virulent vir·u·lent (vēr'yə-lənt, vēr'ə-)
Extremely infectious, malignant, or poisonous. Used of a disease or toxin.
Capable of causing disease by breaking down protective mechanisms of the host. Used of a pathogen.
Intensely irritating, obnoxious, or harsh.