monophthong; simple vowel
Linguistics term for a vowel with a single, unchanging quality, as opposed to a diphthong or triphthong.
Japanese 'a', 'i', 'u', 'e', 'o' are monophthongs.
English 'ai' is a diphthong, not a monophthong.
三重母音 (triphthong) involves three vowel qualities in one syllable, contrasting with the single quality of 単母音.
Compound of 単 (single) and 母音 (vowel). The term is a direct calque from Western linguistic terminology.