contagious or poisonous matter, as of specific ulcers, the bite of snakes, etc.; -- applied to organic poisons.-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.-fig.: any morbid corrupting quality in intellectual or moral conditions; something that poisons the mind or the soul; as, the virus of obscene books.