compound vowel; complex vowel
Linguistics term for a vowel sound that combines two or more vowel qualities, such as a diphthong or triphthong.
The 'ai' in the Japanese word 'ai' (love) is an example of a compound vowel.
二重母音 specifically refers to a diphthong (two vowel qualities), while 複合母音 is a broader term that can include triphthongs or other complex vowel combinations.
単母音 is a simple or pure vowel with a single, steady quality, contrasting with the combined qualities of a 複合母音.
Compound of 複合 (fukugō, 'compound') and 母音 (boin, 'vowel'). The term is a direct calque from Western linguistic terminology.