noun
Linguistics term for a complex vowel sound that glides from one vowel to another within a single syllable.
英語の「boy」の母音は複母音です。
The vowel in English 'boy' is a diphthong.
Monophthong, a pure vowel sound without gliding.
Compound of 複 (fuku, 'compound') and 母音 (boin, 'vowel'), literally 'compound vowel'.