virulence vs virulency

virulence and virulency both are nouns.

Word	Noun	Adjective	Verb	Adverb
virulence	Yes	No	No	No
virulency	Yes	No	No	No

As nouns, virulence and virulency are synonyms defined as:

virulence and virulency: extreme harmfulness (as the capacity of a microorganism to cause disease)

As nouns, virulence and virulency are synonyms defined as:

virulence (noun)	virulency (noun)
extreme harmfulness (as the capacity of a microorganism to cause disease)	extreme harmfulness (as the capacity of a microorganism to cause disease)
extreme hostility	extreme hostility