caseus

Latin caseus meant 'cheese' and is one of the oldest food words in the Indo-European family. Some linguists trace it to Proto-Indo-European *kwat-, meaning 'to ferment' or 'to sour,' though this reconstruction is contested. What is certain is that Romans took their cheese seriously. Pliny the Elder, writing around 77 CE in his Natural History, described dozens of varieties from across the empire — smoked cheese from the Alps, soft cheese from Gaul, sharp cheese from the area around modern Parma.

The word traveled two paths into European languages. The Romance languages kept close to caseus: Spanish queso, Portuguese queijo, Italian cacio (though formaggio, from Latin formaticum meaning 'molded,' eventually won in standard Italian). The Germanic languages borrowed caseus early — before the fall of Rome — reshaping it into Old English cyse or cese, Old High German kasi, and Dutch kaas. English cheese comes from this Germanic borrowing.

The two paths reveal something about Roman trade networks. Germanic peoples were buying Roman cheese long before they conquered Roman territory. The word was a trade good that preceded the military conquest. By the time Angles and Saxons brought cese to Britain in the 5th century, the word had been in Germanic mouths for generations already.

Casein — the main protein in milk, isolated by Swedish chemist Jons Jacob Berzelius in 1838 — takes its name directly from caseus. So does the word casserole, from French casse, a vessel for baking cheese dishes. The Latin dairy word runs quietly through modern kitchens, laboratories, and supermarket aisles.