'Virulency' definitions:

Definition of 'virulency'

noun

Extreme harmfulness (as the capacity of a microorganism to cause disease); "the virulence of the plague" [syn: virulence, virulency]

noun

Extreme hostility; "the virulence of the malicious old man" [syn: virulence, virulency]

From: GCIDE

Virulence \Vir"u*lence\, Virulency \Vir"u*len*cy\, n. [Cf. F. virulence, L. virulentia an offensive odor, a stench.]
1. The quality or state of being virulent or venomous; poisonousness; malignancy. [1913 Webster]
2. Extreme bitterness or malignity of disposition. "Refuted without satirical virulency." --Barrow. [1913 Webster]
The virulence of one declaimer, or the profundities and sublimities of the other. --I. Taylor. [1913 Webster]