Virus \Vi"rus\, n. [L., a slimy liquid, a poisonous liquid, poison, stench; akin to Gr. ? poison, Skr. visha. Cf. Wizen, v. i.]

1. (Med.)
   (a) Contagious or poisonous matter, as of specific ulcers, the bite of snakes, etc.; -- applied to organic poisons.
   (b) The special contagion, inappreciable to the senses and acting in exceedingly minute quantities, by which a disease is introduced into the organism and maintained there.

Note: The specific virus of diseases is now regarded as a microscopic living vegetable organism which multiplies within the body, and, either by its own action or by the associated development of a chemical poison, causes the phenomena of the special disease.

2. Fig.: Any morbid corrupting quality in intellectual or moral conditions; something that poisons the mind or the soul; as, the virus of obscene books.

Source: Webster's Revised Unabridged Dictionary (1913)