Origins
The word 'influenza' is a remarkable fossil of Renaissance astrological thinking, preserved intact in the medical vocabulary of every English-speaking country.βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ It is simply the Italian word for 'influence,' borrowed into English during a severe European epidemic in 1743 -- and it carries within it the medieval belief that epidemics were caused by the influence of the stars.
The chain of derivation is straightforward. Italian 'influenza' comes from Medieval Latin 'influentia' (an inflowing, an influence), from the Latin verb 'influere' (to flow in), composed of 'in-' (into) and 'fluere' (to flow). The Latin root 'fluere' derives from PIE *bΚ°lehβ- (to blow, to swell, to flow) and is one of the most productive roots in English, having generated 'fluid,' 'fluent,' 'affluent' (literally 'flowing toward,' hence wealthy), 'confluence' (a flowing together), 'influx' (a flowing in), 'superfluous' (overflowing), and many others.
The application of 'influenza' to disease arose from medieval and Renaissance astrological medicine. Before the germ theory of disease, epidemics posed a profound explanatory challenge: why did so many people in so many different places fall sick simultaneously? The astrological answer was that the stars and planets, in certain unfavorable configurations, sent down an invisible 'influence' -- an inflowing of celestial power -- that corrupted the air and sickened those exposed to it. An epidemic was an 'influenza delle stelle' or 'influenza di freddo' (influence of the cold), later shortened simply to 'influenza.'
Scientific Usage
This astrological explanation was not considered fringe or superstitious by the standards of the time. It was mainstream medical theory, taught in universities and endorsed by leading physicians. The concept of celestial influence on health was deeply embedded in European medicine from antiquity through the early modern period -- the English word 'disaster' (from Italian 'disastro,' bad star) preserves a similar astrological worldview.
The word entered English during the European influenza pandemic of 1743, which spread outward from Italy. The April 1743 issue of the London Magazine reported on the Italian epidemic and used the Italian term, which was quickly adopted by English physicians and journalists. The word filled a lexical gap: English had no single, precise term for this specific recurring pattern of respiratory epidemic, and the Italian word -- exotic, medical-sounding, and already in use across the continent -- served perfectly.
The abbreviation 'flu' appeared by the mid-19th century, first as 'flue' (1839) and then in its modern spelling. This clipping removed the word's transparent connection to 'influence' for most English speakers, further obscuring its astrological origins.
Cultural Impact
The 1918 influenza pandemic (misleadingly called the 'Spanish flu') killed an estimated 50-100 million people worldwide and permanently elevated the word's prominence in English. Since then, 'influenza' and 'flu' have been among the most commonly used medical terms in the language, appearing annually in public health campaigns, news reports, and everyday conversation.
The irony of the word's survival is notable. 'Influenza' was coined within a medical framework -- astrological causation -- that has been entirely discredited. We now know that influenza is caused by specific RNA viruses of the family Orthomyxoviridae, transmitted by respiratory droplets, with nothing whatsoever to do with stellar alignments. Yet the astrological term persists, used billions of times each flu season by speakers who have no idea they are invoking the influence of the stars.