a vowel sound that starts near the articulatory position for one vowel and moves toward the position for another
A complex vowel sound that begins with the sound of one vowel and ends with the sound of another vowel, in the same syllable.
The word "diphthong" comes from the Ancient Greek díphthongos, which literally means "two sounds." It combines elements meaning "twice" and "sound," reflecting that a diphthong is made up of two vowel sounds spoken together.