monophthong

This term is primarily used in linguistics and phonetics to describe a vowel sound that is stable and unchanging. It stands in direct contrast to a diphthong, where the tongue moves from one position to another during the production of the sound, creating a glide.

In practical usage, the word is highly technical and rarely appears in casual conversation. It is typically found in academic papers, language textbooks, or phonetic transcriptions to specify the precise nature of a vowel's articulation.