Amonophthong (/ˈmɒnəfθɒŋ,ˈmɒnəp-/MON-əf-thong,MON-əp-) is a purevowel sound, or one whose articulation at beginning and end is relatively fixed, notgliding up or down towards a new position of articulation. A monophthong can be contrasted with adiphthong, where the vowel quality changes (glides from one quality to another) within the same syllable, and withhiatus, where two vowels are next to each other but in different syllables. A vowel sound whose quality does not change over the duration of the vowel is called a pure vowel. The word comes fromAncient Greekμονόφθογγος (monóphthongos) 'one sound'.^[1] fromμόνος (mónos) 'single' andφθόγγος (phthóngos) 'sound')

The conversions of monophthongs to diphthongs (diphthongization), and of diphthongs to monophthongs (monophthongization), are major elements oflanguage change and are likely the cause of further changes.

In some languages, due to monophthongization,graphemes that originally represented diphthongs now represent monophthongs.

• Diphthong, also known as a vowel cluster
• Vowel hiatus
• Index of phonetics articles
• Table of vowels
• Semivowel
• Triphthong
• Vowel
• Vowel breaking