Why is the ninth month called September?
1880, from French dossier "bundle of papers," from dos "back" (12c.), from Vulgar Latin dossum, variant of Latin dorsum "back" (see dorsal). Supposedly so called because the bundle bore a label on the back, or possibly from resemblance of the bulge in a mass of bundled papers to the curve of a back. Old French dossiere meant "back-strap, ridge strap (of a horse's harness)."