a combination of two vowel sounds or vowel letters, for example the sounds /aɪ/ in pipe /paɪp/ or the letters ou in doubt 二合元音；复元音；双元音；双元音字母组合 WordfinderTopics Languagec1Word Originlate Middle English: from French diphtongue, via late Latin from Greek diphthongos, from di- ‘twice’ + phthongos ‘voice, sound’.