Most people know that the word flu is a truncation of the more scientific term influenza, but only a few know about the origin after that. Arguably through Spanish, it comes from the Italian word influenza, which comes from the Italian word influentia. This had a distinguishably different definition, one which you may have figured out already: "influence" (except this is particularly in a supernatural sense; the broader influence that we know today evolved in the late 1500s from that word). This is because early people with flu were thought to be under the influence of the stars, so there you go: they had ill omens from above. This is from the verb influere, which meant "flow" or "stream", because the stars were supposed to be emanating a flow of influence. Eliminate the prefix -in and we have the verb fluere, with basically the same meaning (and the origin of fluent, through Latin fluentum, "relaxed"). Finally, this is from Proto-Indo-European bhel, meaning "to swell", making it the distant cousin of other words like follicle, bollocks, ballot, boil, beluga, and hundreds of other words. Anyway, I'm writing this blog post under the influence of the flu, which makes it all the more relevant and whimsical.
Adam Aleksic, a freshman studying linguistics at Harvard University, has been described as the internet's sixth most famous etymologist. He has disturbing interests in words, vexillology, geography, board games, limericks, and law, and he loves writing about himself in the third person.
The Etymology Nerd