The Weighting Game

I was in the shower getting ready for work this morning and the word that came into my head was "molecule". (Long story.) I knew that "-cule" was a Latin diminutive derived from "-culus": we still see both forms in English, rarely, in "animalcule" and "homunculus". It was the "mole" part I couldn't figure out.

I knew that "mole" was a term used in chemistry for a particular quantity of something--specifically, the weight of a substance if there are 6.022x10²³ molecules of it. (I had to look that number up, but I really did know that that's what it meant. It's called Avogadro's Number.) A mole of water, six point oh two two bajillion molecules of it, weighs 18.016 grams. (I had to look that number up, too. I'm not a chemistry whiz.)

But clearly "mole" was derived from "molecule" and not vicey-versey. That didn't help at all.

It turns out to be exceedingly simple. "Molus" is the Latin word for "mass", as in a batch of something, so a molecule is a tiny amount. ("Mole", the unit of mass, is actually borrowed from German "Mol", which is short for "Molekül".)

"Molus", interestingly enough, derives from Latin "mola", "millstone". A millstone is used for grinding things, and so are your teeth, and that's why some of them are called molars. Etymologically, some of your teeth are tiny millstones! Isn't that great?