ɪˈmjuːnɪtɪ

Immunity: Exemption from a service, obligation, or duty; the condition of being insusceptible to the contagion of a specific disease

Our aim is to try and reduce the peak, broaden the peak, not suppress it completely; also, because the vast majority of people get a mild illness, to build up some kind of herd immunity so more people are immune to this disease and we reduce the transmission, at the same time we protect those who are most vulnerable to it. Those are the key things we need to do.

Sir Patrick Vallance, BBC Radio 4, 13 March 2020

We’ve been hearing a lot about immunity lately. Developing herd immunity to COVID-19 suddenly turned into a Very Bad Plan only a week or so after Patrick Vallance, the UK government’s Chief Scientific Adviser, made the above statement. But it will probably turn into a Very Good Plan at some unspecified time in the future, if it can be achieved through mass vaccination rather than mass infection.

The word comes from the Latin adjective, munis, “ready to be of service”, from the noun munus, meaning “service” or “duty”. By adding the negating prefix im- to munis, the Romans derived immunis, which meant “free from service or duty”. And that was the sole meaning of the English word immune until the late nineteenth century, when the nascent science of medicine co-opted it to mean “not susceptible to a specific infectious disease”. And so we now have the medical specialty of immunology, and the practice of immunization.

The Romans also added the prefix com- to munis, suggesting “shared duty”—but the meaning of communis broadened to indicate anything that a group of people shared. From which we derive community, commune (noun and verb) and common (as in, “we have something in common”). From an original meaning of “belonging equally to more than one”, common quickly developed additional connotations—if something was common, there was a lot of it about, and it was a bit ordinary, and maybe even something that could be looked down on as being rather vulgar. Interestingly, common has managed to hang on to all those different meanings for six hundred years. It also assumed duty as a noun, designating the land to which a community shared access, and it’s still used in that sense in England today. For a while, it was also the name for the specific rights that a person had to that common ground—so you had common of pasture if you were entitled to graze your livestock, common of piscary if you had fishing rights, common of turbary for digging turf, and common of estovers if you could gather firewood.

The House of Commons, the name given to the “lower house” of the bicameral parliament in both the United Kingdom and Canada, is so called because its members (in theory at least) represent the interests of the communities that elected them.

Latin communis also gives us communism, a doctrine that rejects all private ownership; communion, a coming together in a spirit of sharing; and the verb to communicate, which implies the sharing of information. And, coming full circle to the word that started this post, a disease is communicable if it can be shared with (that is, infect) others.

Latin munus, meaning “service” or “duty”, acquired another oddly unrelated meaning—”gift”. This may relate to the fact that it was the duty of prominent Roman citizens to finance what were essentially gifts to the populace—public games and performances, financed by the wealthy elite, also fell within the ambit of the noun munus.

Both senses of the word have reached English. If you remunerate someone, you pay them for services rendered. And a municipium was a city whose inhabitants enjoyed the privileges, and duties, of Roman citizens—from that, we get our words municipal and municipality.

Someone who is munificent gives generous gifts; they exhibit munificence. Sadly, several related words have fallen into disuse—if you were carrying a gift, you were muniferous; if you plied another with gifts, you munificated them; and anything pertaining to gifts was munerary.

These handy little words are my gift to you. Let’s get them back into common usage.