Why is the ninth month called September?
1560s, possibly from Old French *baivel (Modern French béveau, biveau), possibly from bayer "to gape, yawn," from Latin *batare "to yawn, gape," from Latin root *bat-, possibly imitative of yawning. If so, the time gap is puzzling. The verb is first recorded 1670s. The noun is 1670s, from the adjective.