Why is the ninth month called September?
1590s, of uncertain origin, perhaps from dialectal French trepasser "pass over or beyond," from Old French trespasser (see trespass). Or from a source related to Middle Dutch trappen, dialectal Norwegian trappa "to tread, stamp" (see trap). Liberman points out that it resembles German traben "tramp" "and other similar verbs meaning 'tramp; wander; flee' in several European languages. They seem to have been part of soldiers' and vagabonds' slang between 1400 and 1700. In all likelihood, they originated as onomatopoeias and spread to neighboring languages from Low German." Related: Traipsed; traipsing.