複ふく母ぼ音いん

noun

diphthong

Linguistics term for a complex vowel sound that glides from one vowel to another within a single syllable.

• 英えい語ごの「boy」の母ぼ音いんは複ふく母ぼ音いんです。

  The vowel in English 'boy' is a diphthong.