monophthong (n.)

A term used in the PHONETIC classification of VOWEL sounds on the basis of their MANNER OF ARTICULATION: it refers to a vowel (a PURE VOWEL) where there is no detectable change in quality during a SYLLABLE, as in English cart, cut, cot. Vowels which change in quality are known as DIPHTHONGS (or TRIPHTHONGS). In some DIALECT and DIACHRONIC studies, a process of monophthongization can be found, i.e. a change in VOWEL QUALITY from a diphthong to a monophthong.