a combination of two vowel sounds or vowel letters, for example the sounds /aɪ/ in pipe /paɪp/ or the letters ou in doubt compare monophthong, triphthong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’.