Monophthong

A monophthong is a vowel whose quality remains more or less stable during its whole articulation, which means there is (practically) no change in the position of the tongue, the rounding of the lips or in the opening of the vocal tract. An example of a monophtong in English is the a in hat.

Monophthongs are distinguished from diphthongs or triphthongs, the last two being in fact combinations of one or two vowels as well as a semi vowel.