Etymology dictionary

virus (n.)
late 14c., "venomous substance," from Latin virus "poison, sap of plants, slimy liquid, a potent juice," probably from PIE root *weis- "to melt away, to flow," used of foul or malodorous fluids, with specialization in some languages to "poisonous fluid" (source also of Sanskrit visam"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 gwyar"blood"). Main modern meaning "agent that causes infectious disease" first recorded 1728 (in reference to venereal disease). The computer sense is from 1972.