diphthong

n union of two vowel sounds or vowel letters, eg the sounds / aI; aI/ in pipe / paIp; paIp/, the letters ou in doubt 二合元音, 复合元音, 双元音（如pipe / paIp; paIp/ 中的 / aI; aI/音）; 复合元音字母（如doubt中的ou）. Cf 参看 monophthong.

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