The Etymology of Virus

What’s the plural of “virus”?  Virii? Viruses? Vira?

My 2nd year anatomy professor was, somewhat like me, a stickler for proper written language. Someone had asked him what the proper plural of “fetus” is, since many of us stupidly assumed it was “feti”, given the word’s Latin root.

“No,” he said. “It’s fetoos.” (Spelling mine; it’s probably meant to be spelled with a “u” with a bar on top, rather than “oo.”) When we looked at him askance, he added: “It’s fourth declension Latin.” My simple one semester of Latin was insufficient armament against such erudition. I conceded.

The question has arisen again in the wake of COVID-19. What is the plural of virus?

It is indeed a Latin noun, so one would expect it to follow Latin pluralization rules. But according to, “The noun virus has a Latin root, but is one of the few nouns that has no plural in Latin. It occurs only in the singular. The English plural viruses (which adheres to the standard rules for forming plurals) is the only way to make the noun virus plural.

Great. So no “viri”…. which sounds like the common Guyanese name of the  very hot pepper, “Capsicum Frutescens.” We call it “wiri-wiri.”

Where does the word “virus” come from?  It sounds like it should be related to “virile”, no?  In fact, in my favourite artificial language Esperanto, the word for “man” is in fact “viro”.

But there appears to be no historical connection between “man” and “virus”… at least not etymologically. Despite the fact that in Latin, virus means poison, venom, or animal semen. Yeah, that last one makes you think of men, no?

The word makes its first appearance in English around 1400 “to refer to pus or discharge from a wound.”  Nice.

According to, virus comes from “poison, sap of plants, slimy liquid, a potent juice.”

But its roots go deeper than Latin and into Sanskrit, as do all good things. It likely heralds from the Sanskrit visam, meaning “venom, poison,” and visah, meaning “poisonous.” There may also be a connection to Zoroastrian languages in which vish meant “poison.”

How does all this help us? Well, it allows us to use “viruses” without hesitation as the proper plural of “virus.” And if anyone says “viri” in your vicinity, feel free to lay down a good old fashioned
palmis caedebat on their ass .