Why is the ninth month called September?
"accustomed, usual," c.1400, past participle adjective from wont. An unconscious double past participle.
"accustomed," Old English wunod, past participle of wunian "to dwell, be accustomed," from Proto-Germanic *wun- "to be content, to rejoice" (cf. Old Saxon wunon, Old Frisian wonia "to dwell, remain, be used to," Old High German wonen, German wohnen "to dwell;" related to Old English winnan, gewinnan "to win" (see win) and to wean. The noun meaning "habitual usage, custom" is attested from c.1300.