Why is the ninth month called September?
1610s, originally a type of dagger; as a steel stabbing weapon fitted to the muzzle of a firearm, from 1670s, from French baionnette (16c.), said to be from Bayonne, city in Gascony where supposedly they first were made; or perhaps it is a diminutive of Old French bayon "crossbow bolt." The city name is from Late Latin baia "bay" + Basque on "good." As a verb from c.1700.