Virus
late Middle English (denoting the venom of a snake): from Latin, literally ‘slimy liquid, poison’. The earlier medical sense, superseded by the current use as a result of improved scientific understanding, was ‘a substance produced in the body as the result of disease, especially one capable of infecting others’.
wiktionary
From Middle English virus, from Latin vīrus(“poison, slime, venom”), via rhotacism from Proto-Italic *weizos, from Proto-Indo-European *wisós(“fluidity, slime, poison”). First use in the computer context by David Gerrold in his 1972 book When HARLIE Was One.
etymonline
virus (n.)
late 14c., "poisonous substance" (a sense now archaic), 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" emerged by 1790s gradually out of the earlier use in reference to venereal disease (by 1728); the modern scientific use dates to the 1880s. The computer sense is from 1972.
VIRUS (among Physicians) a kind of watery stinking Matter, which issues out of Ulcers, being endued with eating and malignant Qualities. [Bailey's dictionary, 1770]
