virus (n.)

late 14c., "poisonous substance," from Latin virus "poison, sap of plants, slimy liquid, a potent juice," from Proto-Italic *weis-o-(s-) "poison," which is probably from a PIE root *ueis-, perhaps originally meaning "to melt away, to flow," used of foul or malodorous fluids, but with specialization in some languages to "poisonous fluid" (source also of Sanskrit visam "venom, poison," visah "poisonous;" Avestan vish- "poison;" Latin viscum "sticky substance, birdlime;" Greek ios "poison," ixos "mistletoe, birdlime;" Old Church Slavonic višnja "cherry;" Old Irish fi "poison;" Welsh gwy "poison"). The meaning "agent that causes infectious disease" is recorded by 1728 (in reference to venereal disease); the modern scientific use dates to the 1880s. The computer sense is from 1972.