Have you ever noticed that a lens looks like an oversized lentil? The fact that “lentil” and “lens” both begin with “len” is not a coincidence; they are etymologically related, though in a slightly convoluted way.
The older of the two words is “lentil”, which refers to a plant producing lens-shaped seeds. It comes from Old French lentille, which in turn comes from Latin lenticula (still referring to the plant). Grammatically speaking, lenticula is a diminutive form of lens, which means “a lentil” (now referring to the seed):
When lenses (the optical devices) were invented, since they looked like seeds of lentil and technical terms are mostly derived from Latin or Greek, people simply called them the same as the seed:
However, English speakers weren’t the only ones who thought of the similarity between the seed and the device. In romance languages, the corresponding expressions are also derived from Latin lens or lenticula, and in a handful of Slavic languages, the words are derived from an unrelated root but are still the same or similar, e.g. Czech čočka, meaning both “lens” and “lentil”.
If there are any German speakers among my readers, they may be thinking right now, “Of course, so this is where Linse comes from!” (Linse means, yet again, both lens and lentil in German). However, Linse comes from an Indo-European root predating Latin lens by thousands of years:
“Lentil” and its translations are some of the longest surviving words in Indo-European languages, being with us since the time the French, the Germans, the Greeks, and most other European nations were all one people speaking a common language somewhere in the Eurasian Steppe. Isn’t that fascinating?