Sequence of two vowels (9)

I believe the answer is:

diphthong

(Other definitions for diphthong that I've seen before include "Ligature of vowels" , "Two vowels pronounced as a single syllable" , "Vowel sound that changes within a single syllable" , "Two-vowel sound" , "Sound of two vowels in one syllable" .)

I've seen this clue in the Sydney Morning Herald.

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