Sunday Rest: nocebo.

A nocebo is the opposite of a placebo: a placebo is a non-active substance administered as a medicine that sometimes has the effect of curing illnesses because people have faith in it; a nocebo is a substance (often a real medicine) that causes unwanted side-effects because people expect to have negative side-effects. (A side-effect that is actually caused by a medicine isn't a nocebo.)

To make things more complicated still, expecting to have side-effects can cause anxiety, and being anxious can cause the body to produce hormones that make it more likely that the body will feel pain.

Now, as you will already have noticed, the thing wrong with the word nocebo is that it looks as if some ignoramus has come along and shoved no at the front of the end of the word placebo to make something that means the opposite. And this would indeed have been an offence against the English language.

As a matter of fact this isn't how the word was coined at all. Its origin is entirely logical and respectable.

But it certainly doesn't look it.

Word Not To Use Today If You Can Help It: nocebo. The Latin nocēbō means I shall harm, from noceō, I harm* (it's the first person singular future active indicative). The Latin placēbō means I shall please, from placeō, I please (ditto). The word nocebo was coined by Walter Kennedy in 1961. He was obviously too learned to guess what pain he was causing to all us ignoramuses.

*Some rather harmful things done as part of a treatment, such as applying a tourniquet, can be termed nocebos, too.