oftenyoudaoicibaDictYouDict[often 词源字典]
often: [14] Oft was the Old English word for ‘often’. It came from a prehistoric Germanic adverb of unknown origin, which also produced German oft, Swedish ofta, and Danish ofte. In early Middle English it was extended to ofte. This developed a form often before vowels and h, which by the 16th century had begun to oust oft(e).
[often etymology, often origin, 英语词源]
often (adv.)youdaoicibaDictYouDict
c. 1300, extended form of oft, originally before vowels and h-, probably by influence of Middle English selden "seldom." In common use from 16c., replacing oft.