virulency

vir·u·lent  (vîry-lnt, vîr-)

adj.

1.

a. Extremely infectious, malignant, or poisonous. Used of a disease or toxin.

b. Capable of causing disease by breaking down protective mechanisms of the host. Used of a pathogen.

2. Bitterly hostile or antagonistic; hateful: virulent criticism. See Synonyms at poisonous.

3. Intensely irritating, obnoxious, or harsh.

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[Middle English, from Latin vrulentus, from vrus, poison.]

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viru·lence, viru·len·cy n.

viru·lent·ly adv.

Thesaurus

Noun	1.	virulency - extreme harmfulness (as the capacity of a microorganism to cause disease); "the virulence of the plague" virulence micro-organism, microorganism - any organism of microscopic size harmfulness, injuriousness - destructiveness that causes harm or injury
	2.	virulency - extreme hostility; "the virulence of the malicious old man" virulence hostility, ill will - a hostile (very unfriendly) disposition; "he could not conceal his hostility"