One of the most dangerous aspects of the coronavirus is how contagious it is: easily spread from one person to another.

That's why so much of our effort in fighting the disease focuses on slowing or stopping the spread: Habits like hand-washing, wearing masks in public, and avoinding touching your face, limits the number of people who gets sick, protects vulnerable populations, and gives doctors and scientists more time to develop treatments and maybe a vaccine. But where did the word contagious come from?

The Romans, like other ancient people, knew that illness could be transmitted from person to person even if they didn't comprehend the microscopic causes of disease. As a result, the Latin contagionem, meaning "touching together" or "contact," often had the negative connotation of contact with something unclean or immoral: something that could corrupt you or make you sick.

In Latin, tangere means "to touch." You can see it in our word tangible — something that can be touched or felt — among others. Tangere originated in the Proto-Indo-European root tag-, meaning "touch" or “handle,” which also gave Latin tactus, "touch," whence the English tactile and intact. Tag- is also the root of taxare, "to assess," which gave us tax and taxation. The prefix con- meaning "together," which appears in many English words — like congenial, concentric, and condominium — completes the word.

The Late Latin contagiosus and its approximate contemporary in Old French contagieus both contributed to the modern English contagious. Closely related in meaning and etymology to contagion, contamination also comes from con-, "together," and tangere, "to touch." In this case, rather than immorality or sickness, the sense is specifically that if a clean thing and a dirty thing touch, the clean thing becomes dirty: contaminated.

Contagious can be used to describe happier things, too. If a person's beaming smile makes you smile as well, that's contagious, and laughter is definitely contagious.

We're running down the origins of some pandemic-related words. Here are a few more:

40 Days of Solitude: The Origin Story of Quarantine

Dom- Sweet Dom- : Homing In on the Origins of Domestic

What's Old Is New Again: The Roots of Novel