The insidious viral is first found as the adjective form of virus in 1948, while its contemporary sense shows up as early as 1989. This is another word where it’s clearer to track forwards in time than backwards.

We can reconstruct the six-thousand-year-old PIE word wisós, meaning “poison”, from an unusually diverse set of descendants: Sanskrit वि॒ष (viṣá), meaning “poison”, “venom”, or “bane”; Ancient Greek ἰός (iós), meaning “poison” or “venom”; Classical Persian بِیش (bīš), meaning “poison”; and Latin vīrus, meaning “poison” or “venom”. Poison has clearly always been an important topic to write about.

As with most medical terms, virus was borrowed into English from Latin (the language of science and medicine) in 1398, with a specific medical definition closer to “pus” or “diseased sputum” than poison. Russian botanist Dmitri Ivanovsky first described the pathogens we now call viruses in an 1892 article, credited in Dutch microbiologist Martinus Beijerinck’s 1898 paper classifying them as distinct from bacteria. Viruses were first visually observed in 1931 and the first flu vaccine was developed in 1945. (The first smallpox vaccine is from 1796! You don’t need to know the theory before you can make useful things!)

Diseases have been described as viral, as opposed to bacterial, since 1948. The infectious analogy was first extended to viral marketing in 1989 to describe a strategy where you get consumers to love your product and convince their workplace to adopt it, using Apple Macintoshes as an example. Meanwhile, the compound computer virus describing self-replicating malware was coined in 1984. Drawing on both influences, the first time a phenomenon was described to go viral on the Internet was in 2000. It had become common parlance by 2004. Viral video was first coined in 2009.