A language stay abroad in French

Two entries here are notebooks, le carnet de vocabulaire and le cahier d’erreurs, and the two nouns are the same noun. Behind both stands Latin quaternum, a gathering of four sheets folded once — the unit a scribe worked in before anyone bound a book. Old French made it quaier, which became le cahier; a diminutive of that same quaier gave quernet, and quernet became le carnet. So French ended up with two nouns from one root and quietly divided the work between them. Le cahier is the stitched exercise book that lies flat on a desk; le carnet is the pocket one — un carnet de chèques, un carnet d’adresses, un carnet de tickets. What makes this worth a minute is that English holds a third copy and hardly anybody notices. « Quire », borrowed straight from quaier, still means a small set of folded sheets and is alive in printing and bookbinding. The four is visible in the neighbours too, since quaternum is the four of « quaternary ». Both notebooks on this page are, if you read them back far enough, four pieces of paper.