Monophthong

A monophthong (/ˈmɒnəfθɒŋ/, MON-əf-thong) is a vowel sound characterized by a relatively stable articulatory configuration throughout its duration. During the production of a monophthong, the tongue does not undergo significant vertical (height) or horizontal (front–back) movement toward a different position of articulation. For this reason, monophthongs are commonly referred to as pure vowels.

Monophthongs are contrasted with diphthongs, in which vowel quality changes (or glides) within a single syllable, and with hiatus, in which two adjacent vowel sounds belong to separate syllables.

The term derives from Ancient Greek μονόφθογγος (monóphthongos, “single sound”), formed from μόνος (mónos, “single”) and φθόγγος (phthóngos, “sound”).